Let's put it this way...what if the guy who started his base with boxing fights a guy with a good chin, and can't finish him? In BJJ you don't need to worry about that, because you just try to submit him. There's no "natural" defense to the proven methods of jiu-jitsu. Plain and simple. Any random schmoe can have a good chin, and land a good enough shot to KO you; however, there's no luck in getting a submission, and no "natural" advantage you can have that stops you from the blood getting cut off to your brain when caught in a submission like a triangle choke.
Also, grappling is much harder to get good at than boxing. Yes this is a matter of opinion, but I'll take the expert opinions of the many great strikers I have met in my time that ALL wish they would have started doing BJJ earlier.
Skills pay the bills. You dont go far at all just having a good chin and lacking in the skills department. The fact that you think some random schmoe can have a good chin and land a good enough shot to KO a relatively good boxer is ridiculous. I'm actually shocked someone would say that. Like Frank Shamrock said getting hit is unnatural. It takes a LONG time to learn how to take punishment. And even at the highest level of MMA you have fighters who are AFRAID to get hit, who close their eyes while punching, who leave their chin out. If you think these guys can land a lucky shot on an elite level boxer you are crazy and you must train with some very mediocre strikers if thats what you base your opinion on. At my boxing gym i've heard some stories that MMA guys like Sam Stout spar a featherweight boxing champion in Steve Molitor and Stout couldnt even lay a hand on him.
Thats like me saying in BJJ, wrestling you're talking about a sport where its athletes have NEVER been hit. I'd say thats a "natural" defense. Many MMA fighters have said you hit a BJJ guy once, he drops a belt, you hit him again he drops another belt. Look at Alberto Crane, great BJJ guy and he couldnt even beat high school wrestler Huerta at his own game.
What sport is harder is a matter of opinion. But in the last 2 weeks i've heard two MMA fighters say boxing is the hardest sport to learn. Frank Shamrock said it on Inside MMA, AA said boxing ALL about strategy and technique whereas MMA is different, and James Warring said boxing is tougher than MMA.
No disrespect to you but there are much better grapplers in MMA than strikers and its no secret MMA lacks the required striking skills to be competitive with even a mid-level boxer or Muay Thai fighter. So if some regional kickboxing champ on a farm in Iowa said grappling is tougher than striking is probably because 1) hes now competing in MMA 2) He has basic level striking skills.
There was a very short clip of Wand/Forrest sparring and let me tell you it was VERY UGLY to watch. And if Wand, Forrest are considered to be high level strikers in MMA than im not surprised at all to hear that grappling is harder in comparison to striking after seeing Wand/Forrest block punches with their face and elbows.
The point is you cant take guys who have reached the pinnacle of grappling and compare the skill level to mid-level strikers. The best strikers are not in MMA. But for the most part the best grapplers are at least a few of them.