When I drove the gti in Durham you could tell between the three different modes straight away. comfort relaxed the steering (for want of a better word), normal mode was normal and sport mode tightened the steering (heavier feel). you could tell on the suspension too in the country lanes I was on. I'm pleased I added it to my order.
Part of my thinking is my S Line suspension would be similar if maybe slightly harsher than the GTI Sport setting and was actually pleased to see Sport was described as 'fidgety' on town roads as that is my experience now and that by placing setting to 'normal' the ride settled markedly so that justifies the choosing of ACC right there.
Think the expectation should be that 'Sport' is a little fidgety on the very indifferent town roads we experience and that there is not anything actually wrong in it being so as that set up is what makes for greater driving experience when get to push it a bit more - But I do live with my S Line suspension quite happily we are always quite critical on forums as we highlight experiences and imagine the GTI sport setting is better still and would probably be more than fine as a standalone still.
With both the ACC and DSG being new and refined versions seems I have picked a good time to jump on board from Audi

In fact having been looking at other versions of GTI and comments in overall forum from MK4-6 thinking of selling our 2nd car a Mini Cooper and going all in on Golf GTI/GTD