I watched these videos last night as it goes Makes for very interesting viewing.Quality rubber makes a huge difference. I have multilink rear end, which also helps on more challenging roads, but I doubt there's a noticeable difference around town. I also have the pressures a touch lower that the manufacturer states, as this seems to be for economy. No uneven wear to speak of.
If your car is wearing Bridgestones, it doesn't surprise me that it's unacceptable. More like brickstones. We didn't realise how bad they were until they were gone from my mum's GTD. Night and day difference. Get yourself some decent rubber. It's the easiest option. Buying second hand wheels etc. is time consuming, and if they're not straight, then you'll get wheel wobble and warning codes on the dash.
I have no doubt that a Leon with steely 15" wheels will ride the best from a comfort point of view, but I bet it rolls over on its sidewalls. Going from 18 to 17 isn't going to make any meaningful difference if you still use hard, unforgiving tyres. Changing to decent rubber will. These videos may help you decide:
UHP tyres 18":
This channel is really informative.
The fact a golf actually has decent suspension probably helps too. Bridgestones are definitely going as a start, just got back from an hour each way trip to do some Xmas shopping with 2 passengers and the ride was shocking especially on the way back. Felt like there is almost zero damping on the rear especially which funnily enough is where the Bridgestones are.
Both passengers actually think I should book it in as in their words ‘that can’t be normal’