Conveniently, that is exactly the stuff you don't need [emoji4]
Meaning:
I don't bother with xp calculations and awards, I award levels when it feels appropriate.
I don't use the CR and ECL type of stuff, since that's useless.
So no wonder the SRD3 omissions weren't a problem - they actually made the game better! [emoji3]
Well, "Can experienced players play their own house-ruled version of the game?" is not the same as "Can anyone play the game?"
Technically, I can play a game with no written rules whatsoever, or only what is in my own head, right? I can jot down my memories, call them the rules and play. I don't technically need rules at all, and never did, right? Technically, it's just a structured "let's pretend," and I can do that without anything from any company.
But, strangely, though none of us have ever needed any rules whatsoever... we all want them and buy them and use them. Thus, the logic of "I can play the game with that if I just ignore things they left out" seems a bit of a blithe statement.
Specifically, for you - you have this thing where you award levels when it feels appropriate. That's fine for an experienced gamer, but, like many house rules, it is really based on knowing the rule first, and then making a planned departure from them.
But, for someone new trying to pick up the game, there's not even a *hint* of how to do that in the d20 SRD, now is there? A new player would look, see all these levels and ask, "Well, what are these things, and how do I go from one to another?" It is not a realistic expectation that they'd just by random chance, hit upon the idea of just going up levels every once in a while, and just happen to execute it at a rate that's particularly pleasing to the folks at the table. They'd fumble around, and have a bad experience, and probably give up.