That's reasonably fair. A lot of things could mess up the classic game, some even earlier than that, but certainly by the time you were using Enchant an Item and it's ilk, there'd be issues. In the classic game. And, not surprisingly since it evokes the classic game so well, in 5e, of course.Generally speaking, the RAW of D&D for all editions of the game starts breaking down around when 6th level spells come online, and it requires a great deal of skill and inventiveness on the part of the DM to not have a skilled group of players with high level characters just running wild with little real challenges.
It's no great stretch with just the PH, either. That's what CoDzilla was originally coined to illustrate.Playing 3e D&D at higher level is IMO mostly an exercise in limiting the chargen options players have available, as if you have access to all the books it is trivially easy to build 3e D&D characters of high level that break the game wide open in various ways.
That got our first 3.x campaign through to level 13 in better shape than usual, yes. The group's "system masters" were either playing fighters or running the game. I guess masters like a challenge.Also, it helps if the players playing the tier 1 classes don't have a whole lot of system mastery and if you don't have fungible magic items in your game so that players can optimally kit up their characters.
True in the classic game, just getting out of the lowest levels is quite a hurdle. But in the WotC era survival into high levels is not that challenging (for the players) unless the DM decides to go well beyond the guidelines...I certainly can imagine higher level play working, and I wouldn't mind doing it at some point, but it's an extremely lucky and dedicated group that can get there fairly if the DM is not just Monte Hall and deliberately powering them up to high level.
That's reasonably fair. A lot of things could mess up the classic game, some even earlier than that, but certainly by the time you were using Enchant an Item and it's ilk, there'd be issues. In the classic game. And, not surprisingly since it evokes the classic game so well, in 5e, of course.
In 3.x, by the time you had 4th level spells you were quite possibly seeing real problems. Thus E6.
But, right or wrong, you just can't say "for all editions" and "6th level spells" in the same breath
True in the classic game, just getting out of the lowest levels is quite a hurdle. But in the WotC era survival into high levels is not that challenging (for the players) unless the DM decides to go well beyond the guidelines...

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.