So you and I have some different thoughts on things, which is cool, so don't take my disagreeing with you as dogging on you, because you're a pretty cool guy. Here are my thoughts on some of the things you post . . .

We do takedown defense (as well as other grabs, etc.) as a regular part of our training regimen, and even sometimes work on being on the ground just in case. Murphy's law and all that. My sifu emphasized both the fear factor in being on the ground, but also that the same training we do for when we're on our feet applies just as well on the ground. I will say we had a guy with years of BJJ from some serious schools come in who was unable to get most of us on the ground.

Honestly? I'm not surprised the BJJ practitioner had trouble taking you guys down. BJJ has garbage training when it comes to take downs. The running gag for BJJ is to land on your back and hope the other guy takes the bait. Someone who practices Judo, Olympic, or Folkstyle wrestling though? They'd be a bit more to handle. That said, if you do mix it up with a BJJ practitioner when you're on the ground, they stand a pretty decent chance. Those guys drill hard.

We emphasize that someone should get lit up long before they get to you, and even if they make contact they shouldn't get you off your feet. With enough training, it works.

Lighting a guy up with a flurry of blows isn't guaranteed to stop them. The human body is actually surprisingly resilient for being such a fragile machine and it can take a load of punishment and keep on going. At the same time, developing good, consistent knockout power is extremely hard to do, especially if you're a smaller person. That's part of the reason why, even on the professional level, in MMA and Boxing most fights in the lighter weight classes often go to decision. If being able to light a person up was good enough, no one would focus on grappling in MMA because no one would risk take down attempts.

About a year or two after that, I tried BJJ a little bit. Honestly, I was not impressed. I couldn't stop myself from being taken down, but because of the relaxation from my Wing Chun training, I was pretty much impervious to joint locks. And this was my ~1 year of Wing Chun against people with like 3 years+ of BJJ.

I'm a bit on the fence with BJJ. On the one hand, I think its actually a pretty deep grappling system. On the other hand though, I think the competition minded training and the rulesets for said competition have somewhat limited the applicability of the style. While it's nowhere near as bad as fencing for example, there are similar signs of evolution where when you train for a certain ruleset it suddenly becomes a min-max development and what you end up with is a style with a few holes that need to be filled back in.

As for relaxing, it only gets you so far. If someone has you in a proper armbar? Relaxig isn't gonna save you. Heel hook and rear naked choke? Same. There are limits to how the body can move and forcing it to move in ways its not supposed to doesn't end well.

I've done aikido as well, but with any of the grappling/throw arts, they only work if the opponent gives you a lever. Levers come from tension. Most people don't learn how to relax in a fight (It's incredibly hard), so most people will give them.

I don't usually say this about most martial arts, but for Aikido, I will. It's mostly garbage. Aikido is based with very linear attacks in mind and it is trained with compliant opponents in mind. In reality against people both trained and untrained, most fighting is non-linear, non-simplified combos, and nobody is gonna just let you throw them around. If you want something that's in the spirit of Aikido but actually works relatively decently, Judo is a much better alternative.

But, I did notice that none of those arts could really handle a punch very well. The guy I mentioned earlier even said they assume in their training that they're going to take some hits while they close to grappling range, which is insane.

See my previous statement about rulesets and such. That said, while an art isn't designed to handle a punch well, once again the human body is surprisingly resilient and can take multiple blows quite easily, especially when the adrenaline is flowing. So someone could quite well get into clinching range, even while taking punches, and get a takedown. So having that mentality isn't really insane, but actually quite realistic. What they're doing is allowing themselves to overcome a very real barrier, the fear of getting hit. One hit knockouts are rare. Getting hit two or three times and having your body shut down is even rarer. Once people realize that getting hit hurts, but otherwise isn't that bad, that fear disappears quite quickly and what you end up with is a person you don't really wanna mess with.

What if the guy has a knife, like you described? What if he hits like some of the guys I train with (Wing Chun punches are a whole different animal)? What if there's 3 of them?

Do whatever you need to de-escalate the situation, otherwise you're likely fucked, even with martial arts training.

So my experience with the grappling arts is that they're fine for competition, and fine against someone who doesn't know what they're doing. But real life scenarios are a whole different ballgame.

That's true for all martial arts. ;)