Sean is right though. He would break them in training, and although their training is tough, hundreds of people survive it. So why can’t Strickland? He may survive but they never would.
When you think about how many ppl survive MMA training on a weekly basis, compared to those surviving SEAL training, it's pretty clear which has the higher breaking bar.
I believe you could train ANY navy seal to make it through a week of training with Sean, even if it took years to train them to that level. I don't think you can train MOST MMA fighters, including a psycho like Strickland, to survive a week of Seal training. Most would wash out due to injury, etc..
Reading Goggins' book where you read about him running for 10s of miles with a knee the size of a grapefruit, after barely being able to stand up initially.... MMA guys don't generally have that kind of resolve. They respect injury and limits waaaaaay more than Seals do and it makes sense. One is paying for a gym membership to hopefully be great, and one is trying to survive with his life and his buddies' lives. The stakes, and the mindset that aims for them and that overcomes them, is very different than the mindstate of most MMA athletes.
That said, that seal would prob never become MW champ of the world due to lack of specific skills and the time to learn them, so Sean can pride himself in his learning and ability. But when it comes to sheer grit? He's not out-gritting a seal. Goggins did pull ups until his palms were half ripped off of his hand (google the pics). MMA fighters are NOT DOING THAT, lol. They know when to stop. Seals may not know when to stop because when you're facing life and death, not knowing when to stop might be a useful skill, unlike when you're fighting for a prize.