I don’t personally have any issue with them. I won’t claim they’re the most comfortable seat in existence but I managed two return trips from London to Dundee with no issues last year and countless shorter journeys.
I agree, even though my rump is not as well padded/upholstered as it used to be having lost weight last year I don't find them uncomfortable.
In general, I would agree with the above comments but these ones where the padding has collapsed around the seat cross support are quite a different experience, believe me, I've sat on one.
Fortunately, the problem is restricted to a minority of seats....so far....but I think it's fair to assume that they are coming to a carriage near you soon!