Lanefan
Victoria Rules
Sorting out what came with what level has been a headache since 3e; I see that, along with a lot of other character complexity added during the WotC era, as a bug rather than a feature.The only real problem with level drain is that it's much more difficult to enact in 5e than it was back in AD&D, which didn't have new abilities every level, and isn't useful with milestone leveling.
There's no reason why level drain can't work with milestone levelling: the drained character is simply a level behind at each step (or more if multiple levels were lost) until a high-level Restoration can be found. This does, however, point out one huge issue with milestone levelling: there's no 'J-curve' to allow lower-level characters or henches to catch up.
If 5e's my starting point the two bolded pieces are directly synonymous.Now here's the second question: Would more item and gear destruction actually make for a better game? Or simply a harder or more punishing one?

If the players also like getting new items (IME nearly all of them love it) then yes, as it allows for more item turnover. Over the long run, gain 10 lose 8 is far more fun and interesting than gain 2 lose 0.What do the players get out of destroying their property? Even if the point is to make the game harder, it should at least make it more interesting in some way. Does this rule accomplish that goal?
Nerfing spell slots makes the game more fun for the higher-level non-casters, perhaps at the expense of some fun for the higher-level casters.Because that's what we're talking about: house rules to make the game better. Does destroying property and nerfing spell slots actually make the game better, meaning more fun for everyone?
That's good on your players, but I'm inclinded to think they're something of an outlier group in this way.See, I think it might in my group. When the silvery barbs spell came out--it's horribly overpowered, it was the players, not the GM, who said no to it. I brought up the idea of incorporating the 5.24 weapon properties to the game before I really looked at how they work, and they seem really unbalanced to me (at least in a 5.14 game) so I was quick to say "whoops, I didn't realize they were so powerful, my bad."
When things aren't balanced*, there's usually only two ways to fix it: nerf one or boost the other. As I've already seen more power creep over the years than I'd really like, my first thought these days is to nerf some things down a bit.It's not necessarily power creep when it's simply more options.
* - and for me to notice or care, it's got to be really out of whack.

If these things make the warrior better and-or more versatile at what they do than they were before, it's power creep.For instance, in Level Up, martials get maneuvers. The lower-level maneuvers let warrior-types briefly cause some condition (the target is tripped, shoved, disarmed or something like that), let the warrior reduce the damage they take, or give the warrior some extra movement. There's a saving throw involved, so it's not an automatic effect, and some take the place of doing damage entirely. And there's really nothing stopping you from giving adversaries these abilities as well.
I don't see this as a power creep at all. It's just things for fighters to do that aren't just "I hit and do 9 damage."