Big 3 just refers to the core of any given team. The Wizards have a Big 3 of Wall, Beal, and Nene - that doesn't mean they're on the same level of Miami's Big 3.
And it's relative: he's saying those three guys are as important to the Clippers as the three most important players on any other team. It's not absolute, i.e. "my Big 3 are as good as the other Big 3s in the league."
It's similar to how a team designates a specific player as their cornerstone by giving them a max deal. Wall isn't as good as Durant, but to the Wizards, he's just as important as Durant is to the Thunder. The max deal isn't meant to say "we think you're as good as other people who've gotten max deals," just "we feel you're as important to this team as other max players are to their own respective teams."
Like I said before, it looks like people overanalyze anything Doc says just to find more reasons to hold a grudge against the guy. It's very ex-boy/girlfriend-ish.