The Rock is the highest paid actor in Hollywood, either him or RDJr, not sure, but in 2007 he wasn't on track.
I guess he would've debuted in 2009 based on his schedule. Brock Lesnar unified the HW title at UFC 100 in July defeating Frank Mir.
I think he could have been solid. He has an college football background, crazy strength and athleticism. He wouldn't have been a GOAT, but it would have been exciting. He's had one hell of a career though and most definitely went the most lucrative route. The Rock is today's biggest action star.