I'd say for sure over 50%, MMA isn't at that level as if yet where it has to enforce doping rules like others.
They're not making nearly enough cash as the big boys, MLB, NBA, Boxing, etc... But once that day comes I'm sure they'll come down super hard on their athletes. I mean that's what it really comes down to, $$$.
Let's use MLB for example, if you pull back the layers it comes down to $. The more excitement the more money comes in, everyone loves to see huge power numbers. Guys hitting the ball out of the park. Which in results in increased ticket sales, fan gear sales, and viewership.
That's when other owners and GMs catch on and start "hating". Mad that other teams have much more cash flow, this has been going on before the days of Barry Bonds, Rodger Clemens, Rafael Palmero, etc...
In the end it's all about money!