You picked your race, class, kit, etc. And then you had specialty classes like Ninjas, Shaman, and Psions. Then there was Multiclassing and Dualclassing as separate concepts. Then there was 2e Gestalts and other rulesets. And don't forget that class kits tended to get stuff at various levels, which sometimes interacted spectacularly with multiclassing depending on your DM.
Skills and Powers, Combat and Tactics, Spells and Magic,m High Level Campaigns, the aforementioned Complete series, Encyclopedia Magica volumes 1 through 4, Wizard's Spell Compendiums 1 through 4, Priests Spell Compendium 1 through 4. Fighter, Wizard, Priest, and Thief's Player Pack. And then there were all the settings which introduced new character options and design structures and narrative settings to be genre-specific... and also Planescape/Spelljammer so you could take your Dark Sun character to various other worlds. (Not recommended due to power levels, but lots of people did it, anyhow!) Don't forget Diablo 2 introducing new mechanics and the various secondary-progression mechanics designed around fealty to a given organization that you gained as you leveled.
There was a TON of stuff you could get over the course of leveling depending on your specific build. And that was -inside- the lines. That's not including the homebrew stuff that kept getting piled on over the years.
Certainly more toward the end of the AD&D 2e Revised period... but that's just how snowfall works.
And hey. Don't forget WotC making "The Compleat Artificer" for 2e as a 3rd party product. Because 3rd party publishing was a thing at the time. Though mainly it was Mayfair Games, I'll grant you.
Character-Creation-Heavy D&D games were a thing well before 3e.