What I think is going on category
When I talk about "internal" styles I am for sure putting Xing Yi/Hsin-I, Tai Chi/Taiji, and Bagua in that category. Those are the internal Chinese martial art trinity. I am unsure if I am supposed to put Daito-Ryu or Aikido in the same category. Anyway all of these arts make a great deal of fuss about "developing" energy. Specifically they talk about chi/ki. Depending on the translation it gets referred to as almost a commodity/tangible that flows, rather than just in terms of physics. I have however met enough internal stylists who could in fact hit hard and "felt" strong as fuck when they applied or resisted force, so something was going on.
The internal arts generally pay a lot of service to everything being a "whole" body movement. Not in the Dan John "body is one piece" sense but in the "every molecule" has to be unified in purpose sense. Many adherents even talk about re-educating or changing or bodywork as what they are doing. The Chinese systems talk about jing, being the power created. Actually I think there is a prefix that indicates unified power but I don't practice any of the right pajama fighting to have that drilled into my head. They hold that any tension or "wrong" movement breaks this up. Conversely they say "external" styles use segmented or sectional power. I know it looks like George Foreman got every part of his ass into those punches, but that qualifies as segmented to there way of thinking. So we have the wrong kind of jing. When they hit/project power that is fajing or peng jing depending on stuff. Peng is warding off I think and Fajing has more to do with hitting if I remember correctly.
Anyway, they make a huge point about unity and economy of motion. What I really have witnessed/felt is that they place a shit ton of emphasis on mechanical efficiency when applying things, to the point of what looks like the detriment of "when shit goes sideways" robustness. You may have just read that as they don't spar enough and it gets ugly when they try and that might be the right of it at least part of the time.
I know you have a karate background as far as TMA goes. If we accept the Tsuri-te and Naha-Te delineation that some of the Okinawan karateka use than Tsuri-te striking is the whole "crack the whip" style of punching and kicking where you are twitching/pulling back at the last instant. That looks similar to what some Chinese stylists call fajing. Here is a video of Erle Montagiue because if I asked you to write a fictional hippy, Kiwi, kung fu stylist you couldn't come up with anything like him and still be believable. He has a "family band" like the Scooby Do cartoon, side note they aren't bad at all.
and really the home made music video isn't bad
Different Fai-jing demo from Sam Chin
now, that may look like a bunch of arm waving. There is that. Watch the twitch in his pelvis/low abdomen with the movements (dantien is worth talking about here) and how stable his legs are. Notice that the twitch's direction.
Naha-te would be pretty much what we would think of as normal striking mechanics.
I read an opinion of an okinawan karate master that was a huge exponent of the superiority of Tsuri-te style striking that admitted that while it was supperior, the practitioner tired out quicker. So the "sport" form of naha-te striking was popular in contests.
The discussions I have had with internal arts practitioners tended to focus a lot more on
internal vs external and what is "real" aiki/jing than specifics of punching. Other that to say they were very much not impressed with the way I do it.
What I think are the differences are the fact most of the internal style strikes I have seen were demonstrated from a "feet first"/ideal stance and footwork position. That isn't a criticism, a demo is just that, Essentially if the "base" isn't there then there is no punch. We might say similar in boxing, kickboxing, combatives, or some forms of karate but if we are honest I bet we both have put people on queer street with a less than ideal blow. I know I have, and not throwing a punch because you are not ideally "set" isn't a religious point for external styles.
If you watch the fa-jing striking in the videos above it also becomes kind of obvious that if the target magically disappeared, the strike would look pretty similar. If you a heavy bag magically vanished right before you hit it, for damn sure you would be struggling to recover/pull the strike in. Now, the opening wouldn't be huge, but we know it would be there. The fact that we pretty much accept that as doctrine is why we learn things like slipping punches. We watch the absolute best punchers in the world, pro boxers, miss and pay for it.