Have you actually used a pace partner? (or do you work for zwift?)
They very much definitely do not behave as you indicate. Firstly if my W/Kg is all over the place, so is theirs, not hard to test. Other people have shown graphs from their trainers showing the wild fluctuations in power in output required to meet pace.
I am 80 kilos. and the problem here is that they slow down so much a man who recently nearly died of heart failure (me) finds it ridiculously annoying.
And the changes in pace do not automatically reflect a change in gradient. If they behaved the way you suggest then changes in pace wouldn’t be a problem as when we hit a hill the pace partners reduction in pace would more closely mimic a normal rider and would gradually vary as the gradient increased.
The changes in pace are on/off and some are in odd places and seem like they have been crudely drawn into a set pace program that is the same on every lap. D deisel slows down half way down the hill to the italian village as if he is expecting to slow down when he hits the cobbles (so you overshoot them significantly going into the sprint) and then on the way out towards oceans drive he starts speeding up again going uphill.
I have since revised my views on this anyway, I think zwift team have actually put significant changes in pace into this to make pace partners somewhat similar to a spin session and probably made these more dramatic on D/Deisel to gear this towards those riders, however the difference is that they have overlooked the necesitty for an audio or visual indicator of changes to the pace.
It’s less noticable on C/Cadence but still you see a marked difference in power output as soon as the gradient hit’s 1%, however as the change in pace is more modest, most riders just let themselves overshoot her on the hill and then let her catch up on the flat. The whole pack is generally miles in front of her on the hills.
What would help with D/Deisel is some shout outs. I’m smashing it now! or something like that. Just so you know to start building up the speed because you cannot see behind you where they are and the change in pace.
Overwise, you’ve just gone way out front of his dawdling ass on the hill, and whilst scratching your crack waiting for them to catch up you can easily be dropped to the point where you have to start plowing in 4W/Kg or more for a fair amount of time to keep up. If you are trying to avoid over working yourself this gets pretty annoying pretty quick.