This week brought perhaps the worst episode of Derek yet. A young rapper called Deon (Doc Brown) came to Broad Hill care home to do community service, provoking the expected reaction from characters written by Ricky Gervais: awkwardness around a black man. Mentally vulnerable helper Derek (Gervais) touched Deon's hair and noted that it was curly, while crass drunk Kev (David Earl) tried to appear cool – "Blacks and whites unite!" - but then spoilt it by slagging off the "Chinkies".

Once Gervais had got that off his chest, Deon became a stooge in another sermon about kindness and respect for the aged. He'd turned up, unnerved and repulsed by having to interact with the elderly, just in time for a talent night at the home. Even naïve Derek would, if watching the show himself, have stood up after ten minutes and said: "Oh Christ, Deon's going to perform a heartfelt rap at the end about how he's changed his mind because the old folk and their carers are so inspiring, isn't he? Clearly he is. Yeech."

Derek would have been right. Deon also chipped in with a speech about how he'd realised that men in the home had fought in the Second World War, and that this trauma was more serious than the things he and his tough mates fight over. Meanwhile Derek confided to the show's unseen documentary-maker, ie directly to us, that he just wanted to make the residents happy, because they didn't have long left and every minute was precious. When Deon had done his rap, Derek said it was brilliant. Deon replied: "Nah. You're brilliant, bruv." 

Jealous, snide critics are obsessed with Derek because they find its emotional manipulation so insultingly basic, they wonder how anyone ever concluded that it would work. Has Gervais lost it? Is he lost without Stephen Merchant? They also like to discuss what Derek tells us about Gervais's character: is the whole project an attempt to make us forget when Ricky spent ages unrepentantly using the word "mong" as an insult, because he's realised his apology came too late and his excuses didn't make sense? Tweets and interviews are combed for evidence of a superstar ego gone sour.

On the other hand, Derek's hardcore acolytes – it gets 1m viewers, which isn't great, but isn't as bad as many people hoped – think, in a nutshell, that because compassion is important and care homes should be invested in and celebrated, a show that says this is a good show. Whether the message is unbelievably heavy-handed or not doesn't matter.

Both camps will have looked forward to The Making of Derek (Wednesday C4; 4oD), which went out after this week's episode. It had self-serving scenes that were forgivable in a programme aimed at fans: at one point a series of supporting actors took turns to say how pleasant the show was to work on, and how nice Ricky is.

Gervais himself discussed the character of Derek. "He is kind and sweet and sincere," Gervais said. "So he's got to be scruffy, he's got to walk funny, he's got to have bad hair, he can't be that bright. Because then kindness comes along and trumps it all." Wait a sec. Why does Derek have to be like that? Isn't it a cheap Forrest Gump device to get away with simplistic, greetings-card sentiment, and make a "mong" the hero? No time to unpack that fully, as Gervais moved on to the show itself.

David Brent had a gulf between what he thought he was communicating and what he was really telling us, whereas everyone in Derek says exactly what they think. "That is the difference between this and traditional sitcoms - there's no level of irony, no juxtaposition [sic] between what people say and think and how we perceive them, which makes it sweeter and nicer and different."

Here is the essence of Derek. Gervais thinks he's refining the dramatist's art, not abandoning it, by making his characters bluntly state their agenda (and the show's) at all times. Yes, to most viewers it kills an emotional pay-off stone dead if you head straight there with no twists and turns along the way, but it's done like that intentionally.

It's almost as if Derek the programme is like Derek the character: completely guileless and hopeless at the task in hand, but well intentioned. The trouble is, it's a plea for sensitivity by a man with a long and ongoing record of insensitivity. (Incidentally, this week's was another episode in which Gervais, who says the whole point of the show is that Derek's kindness makes him admirable, forgot to write in any scenes where he does something kind.)

Much of The Making of Derek was taken up with ribbing Karl Pilkington, who is actually the best thing about Derek by far but was now back to playing his character from An Idiot Abroad, ie an object of Gervais's laughing, vaguely bullying ridicule. The jarring sight of Gervais in fits at Pilkington suffering indignities on set, which meant Gervais was dressed as Derek at the time, summed up why Ricky's work will continue to fascinate us, even if it keeps sliding further and further into mush.

One criticism of Derek that wasn't made so much this year – washed away by the show's flood of sentimentality – was that Ricky Gervais should have cast someone else in the lead, because he couldn't stop himself giving Derek the odd David Brent tic. A glance at the camera here, a note of irritable (and for Derek, out of character) arrogance there. Episode two had a scene where Derek became annoyed that an old woman was standing in his shot.

Oddly enough, that came to mind watching Sue Perkins in the first episode of her long-awaited sitcom debut Heading Out (Tuesdays BBC2, iPlayer). The central character was Sara, a 40-year-old vet, afraid of commitment and very afraid of telling her parents she is gay. Except it wasn't Sara up there, it was Sue Perkins. The wry rhythms, the crafted wit tempered by stuttering diffidence, the coy friendliness twinkling through that protective fringe: Sue Perkins.

So you might say, well, that doesn't work. We don't believe it's Sara. Unlike Grandma's House or Seinfeld or Ellen, the star isn't playing someone with their own name. Perkins isn't meant to be herself, but she inescapably is because we know her too well, in a way most actors cannily never allow.

The solution, in theory: cast someone else. But this wasn't an option, partly because Sara was totally Perkins in script as well as performance, but also because such a thin alter ego let our affection transfer easily. You like Sue Perkins? (Yes.) Then you'll like her playing a woman who looks and sounds the same.

Lose her presence and you'd lose the show's considerable charm, since the supporting cast were mostly struggling as caricatured oddballs: Dominic Coleman as a neat freak, Joanna Scanlan as a bellowy, hockey-sticks life coach hired by Sara's friends to help her come out fully, Mark Heap very Mark Heapy in a bit part as an officious pet-crematorium manager.

Nothing felt real, particularly the digression when Sara played netball and the opposition performed a fearsome dance routine before the game. "It seems to be some sort of inner-city, asthmatic Haka," said Sara, exactly as Perkins would in a documentary or panel show.

The Sara/Sue thing can't sustain Heading Out for long. Sara needs to stand on her own, even if it's through Perkins revealing parts of her own character that the fans haven't seen before, and the dialogue needs to sound a lot less like the carefully written words of a presenter. So it was pleasing to see a glint of this in episode one, when Sara met a potential love interest (Shelley Conn) in the park and ineptly chatted her up.

Viewers nervous about this being a "lesbian sitcom" were probably waiting for one of them to announce that they were gay, but nobody needed to because the writing and acting were nuanced and true. Sara and Sue were both out of their comfort zone - and rising to the challenge.

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