It isn't uncommon to see a fighter with a wrestling background knock out a striking specialist. Chuck Liddell was known for his devastating stand-up even though his background was wrestling. King Mo, Josh Koscheck, Jimmy Hendricks, Jose Aldo, Jon Jones and a whole lot of other Top 10 Fighters came from a grappling background.
It could be because striking came naturally to these fighters allowing them to excel at a rapid pace. Or that small gloves and takedowns/clinch change the standup game in MMA completely. But it could be because grappling-based martial arts have a huge strength component which increases their potential to produce power when they began to practice striking techniques.
When training with weights, strength is the most important fitness parameter for beginners. When practicing sport, power is the dominant fitness parameter. The law of specificity says something is wrong. Why are we trying to develop strength, when our sport calls on huge amounts of force to be developed rapidly (strength is the ability to produce force regardless of movement velocity). Strength is a component of power and when you increase an athletes absolute strength, their power producing ability also increases. It doesn't necessarily mean they will be more powerful, but when they begin power training, they have more power to unleash.
Grappling based martial arts have a huge strength component. Holding your opponent down while he tries to escape, grabbing a leg while your opponent tries to sprawl or squeezing onto a choke requires huge amounts of muscle activation. It is also common for coaches in wrestling to prescribe strength training to their athletes. They have done this for years. In contrast, striking is mostly about speed and power. Being able to deliver a forceful blow with speed is the ultimate goal. This is combined with most coaches advocating their fighters don't lift weights because it makes them slow (which is wrong).
For fighters whose origin lies in grappling based martial arts, there has been a huge amount of strength developed. When they begin to integrate striking into their training schedule, they have so much power to unlock because there strength levels will be higher to fighters with a striking background. Some bias exists because my personal background is Brazilian Jiu-Jitsu, but it does explain why so many grapplers pack a heavy punch!