I do have some admiration for trying to tackle difficult subjects but by not being able to see Ricky and Karl in any other way than their usual characters, it just doesn't really work for me.
I'm not saying Ronnie Barker could've made this show but he had that ability to be totally convincing as different people as a character actor. Performing Fletcher in Porridge and Arkwright in Open All Hours during the same period a case in point.
When they made The Office they were insistent on actors not being well known so it became believable but they obviously don't have that luxury any more.