I don't think any organic team has won the title in a long time. Even with the Bucks Holiday & Lopez weren't drafted by the team. There's probably more but I don't feel like looking at their roster from their title season right now.
I consider the Warriors to be pretty organic, at least as far as their core pieces, especially their big 3. No team does it completely organically. Might have to go all the way back to the 60's or 70's to find one...and even then I'm not sure you'd find a completely organic champion.