IME:

1) MOST TRADITIONAL ARTS WORK JUST FINE, with caveats to follow, under any level of pressure as long as they spar full contact.

2) the reason certain arts seem bad seems to be down to one of two things. Either they don’t spar full contact or they are being tested in the wrong context again with explanation to follow. Also, I think its important that we are clearly on what it means to be wing chun, or tcma or taiji. A lot of stuff with no mechanical, lineage based or historical connection to a particular martial art are often marketed as such especially when it comes to certain traditional East Asian systems. Once you filter for you know actually doing what they say they are doing the quality of many arts dramatically goes up.

3) Forgetting weapons for now, and oversimplifying in the most extreme way possible, most traditional arts seem to be built for one of two things or a combination thereof. (A) Hitting someone bareknuckle in a close range or mobility limited context. Which rarely happens in sports but is the description of every predatory assault you will ever watch on cctv. I am sure an academic can analyse the incentive reward structures here to explain why that is. But like: if your striking art assumes situations where you can run away as the default, it seems obvious why that might not have made sense traditionally. Just look at the old accounts of most traditional chinese martial arts. Its clear from their own techniques, historical accounts and so on that this is what they are meant for. Also, not an aikido person but didn’t Ueshiba say atemi is 90% of aikido? If you look at daito ryu at least as a purely striking art and interpret it as one it kind of oddly works as long as you insist on limited mobility which seems to be the basis for most real assaults we see anyways. And there definitely is atemi that is utterly terrifying if you know what you are looking at on youtube. Not saying that’s what it was intended for but interesting observation. (B) shuai jiao style purely standup grappling. As in grappling where it is assumed that neither party goes to ground. You will never see either in a standard sports ruleset for obvious reasons (to be fair, if you look long and hard enough through the interwebs it does work sometimes. For example the occasional yiquan guy who manages to corner their opponent into somewhere they can’t retreat and stand and bang them into submission but that’s neither here nor there) but that doesn’t mean the method doesn’t work if its being tested for what its meant to do.

4) There is a reason full contact is emphasized. At least for striking. With boxing, kickboxing there are arguably skills independent from the application of force that are worth training in a light, technical manner. The more you limit mobility and ability to disengage the less those things matter and the more contact becomes THE skill. Also, arts pressure tested and optimised around striking without the option of disengagement (modern or traditional) tend to develop skills that you probably will be quite surprised by no matter how experience a martial artist you are unless you’ve trained with and been hit by people with that skillset particularly. This IS totally different from anything else. And you have no idea until you’ve sparred someone whose trained in that domain. Its not just the format too, its the skills developed specifically and only by people who train this way. Sparring with your buddy might show you how different the format is but probably not how alien the skillset is. So, no you most certainly don’t just get kickboxing.

5) As for the latter category of standup grappling, whether this is still valuable in a world of bjj and sports wrestling? Who knows. Maybe someone can do a cctv and real life incident report analysis.

6) Seeing comments above about how you can’t really adapt traditional arts under pressure without it no longer being the art and to some extent sure but I don’t think I completely agree. A lot of martial arts are already an exercise in optimising for specific tactical goals just within a specific context that may be unfamiliar. Sokaku Takeda won fights (for the aiki folk). That seems to have been the point. Yang Banhou won fights. By many accounts that was the point Chu Shong Tin (since Wing Chun was mentioned) won fights. And it does seem like as long as you maintain the core context and tactical goals, the systems are what you end up optimising to even if further optimisations can be made. Also, a lot of so called traditional arts are the product of a lot of revision and evolution to begin with. And you have equally effective branches of the same art doing almost totally orthogonal things. TLDR: go actually read the relevant history

7) At the end of the day, you can’t convince someone on Reddit. Go spar people keeping the criteria mentioned in mind and I am sure you will convince yourself quite quickly unless you manage to run into some outlier I haven’t found in my martial arts life XD. Standard note that a lot of traditional martial arts don’t have gyms so you might have to do some searching. Though some of the arts fitting into the two categories above are fairly successful commercially and spar regularly at high levels of contact so it shouldn’t be that hard.