Micah Sweet
Level Up & OSR Enthusiast
TSR did a pretty good job of being everything for a while IMO. Long enough to amass a huge stockpile of diverse and varied product.The game was easy to learn at lower levels because it told you exactly what you could and could not do. That's far different from being able to tweak combat or add homebrew customizations. The interaction and details of powers was too complex to allow much of either.
Or you could let 3PP do it while you focus on the core rules. Which is what WotC seems to have done instead of the TSR model of trying to be everything and failing.