Isn't this whole thread a 'no true Scotsman' argument?
I think the notion that D&D died with TSR is, honestly, patently ridiculous on its face, as is the notion that nobody plays it the same way they did in TSR era D&D. Heck, I am still running the same campaign that I was running then- my entire gaming history consists of one long megacampaign that spawned a second long megacampaign during the 2e era. There are even some 1e pcs around who have transitioned all the way up into 5e as deities.
Besides a few mentions of IP and repetition of similar fantasy tropes, there was essentially no connection between 3rd edition and any other TSR product.
Ability scores; alignment; AC; hit points; attack rolls; saving throws; most of the spells and monsters; settings such as the FR, Greyhawk, Ravenloft, etc; the basic concepts of the game.... I think there are far more similarities than differences.
Here are some of the biggest differences that I was hung up on when first learning 3rd edition:
1) tactical movement on a grid
Old school D&D arose from wargaming, which might not have always used a grid, but did in some cases; heck, if you look at the 1e DMG's example of play, you'll see reference to the pcs indicating where they move on a map. And not all 3e and later games were played on a grid- I played theater of the mind in every edition at least some of the time, and with the pandemic, we've switched to it pretty much entirely (and pretty seemlessly).
2) attacks of opportunity (for nearly everything)
They weren't called that, but again, look at the 1e DMG's example of play- when the pc grabs the spider that landed on her, it gets a free attack.
These were new, but so what? Every edition had new stuff. Did you feel the same sense of disconnect about "granted powers" for specialty priests in 2e?
This has always been a thing. It just changed methods from edition to edition- starting in 3e, it moved to a balance by level rather than by xp total.
Monster level in earlier editions.
6) 0-level spells, cantrips, and ever-present spells
1e had cantrips, and at will spells weren't a thing until 4e. Yes, this was a big difference.
I give you the 1e bard.
8) the d20 DC system for skills (that took away all DM rulings, as everything was codified)
The very first thing in 3e was Rule 0- basically, empowering the DM to make whatever rulings were required or desired.
9) character wealth by level baked into the system
True in 3e and 4e only.
Anyone else realizing this?
I strongly disagree with the basic premise here. Yes, every edition is different. That was true in earlier D&D too. Remember race as class, or race/class restrictions, or level limits, or maximum and minimum stats by race and sex? Those all changed or vanished over time long before the WotC era. In some cases, they even changed within the course of one edition (hey, now I can play a dwarf cleric as of late 1e!).