Where has it been said that there will be 5 cars running between Swansea and Manchester/the North? Ive only seen it on here, no official document.
The Manchester trains tend to do Ok as 3 cars whereas 2 cars are often crowded, especially at peak times. 5 cars would be overkill most of the day. It's been publicly announced in the franchise plans that there will be increased frequencies on the marches with the addition of 2 hourly Cardiff-Liverpool services from Dec 2022 which should increase capacity overall and ease the demand on the specific peak busy services.
Nothing 'official' as in TfW-branded that I'm aware of, but the July 2018 'Modern Railways' stated that a sub-fleet of 14x3-car CAF Civity units would have 1st class for Manchester-Swansea with 2-car units attached and detached at Swansea to maintain through services between W. Wales and MAN. That bit
wasn't a direct quote from a TfW spokesperson as far as I'm aware, but if it's just a rumour it's a rather more widespread one than just this forum.
That diagram Is one which will eventually be a 67+Mk4 but currently booked 158 IIRC.
Which would explain both the loco-hauled timings and the present lack of first class
Another possible explanation is that, at one point at least, the diagram was planned to be worked by what is currently the north Wales coast (Manchester) mark 3 set (which is of course standard-only).
In other mark 4 news, TfW customer relations have answered my query about possible extra mark 4 sets by saying that it is still just three 4-car rakes (12 carriages) planned at the moment. Then again they also implied that there would be three standard and one restaurant/first class coach, which means either the customer relations pepole are assuming the same formation as the current mark 3s or the plan has changed and they will now be refurbishing the interiors. They "expect to see them in use for the May timetable and initial staff training has started ready for when they are passed to us for use" although that might have been referring to Cardiff-Holyhead in May which if so leaves open the possibility of them being seen on the Manchesters prior to that.