Yes, I understand that we're still in a place where TH9s can prey on TH8s. But to me that's just part of the game. Perhaps the loot penalty could be increased a bit, but on the other hand if we restrict attacks to same-TH only, upgrading Town Halls becomes even more disadvantageous, as a new TH9 (which has no more capabilities than a max TH8 until it can begin some upgrades) now must face TH9s only that it probably has no way of defeating. This is going to remain the case for a long time, until it can upgrade army camps, spell factory, laboratory and a few troops (which the new TH9 isn't in a very good position to do).
Yes, clan wars do get more difficult as you progress due to your base level factoring into matchmaking. But that's okay in my opinion, as that's an optional part of the game. Not many people that I'm aware of use clan wars as their primary source of income for upgrades. In general, though, the game shouldn't get harder simply because you upgraded and became stronger; the fact that you became stronger should give you additional ability to progress in the game (which would therefore become harder). And while I agree that you shouldn't necessarily be forced to progress, adding incentive not to do so is bad (in my opinion), especially since there is no way to un-progress. Having already upgraded shouldn't be a regrettable decision.
The ideal situation in my mind is a game where upgrading has zero downside and people are fairly matched based upon progression. We're a long way from that, I know, but I actually think matching on Town Hall was a step away from that. It was probably necessary due to the abuses of the old system, but I would have hoped for a more equitable solution that still allowed people to reduce the game difficulty for themselves if opponents are too hard. Right now that's nearly impossible to do, which means people who have progressed beyond their skill level are simply going to quit the game after a while.