Olympic fencing obviously sacrifices something, but as a layman I'd have trouble describing it.
Kendo uses wooden swords, does it sacrifice anything else? Would practitioners be proficient in HEMA and vice versa?
Another widely practiced sword art is stage combat. Obviously it has a different focus, but I wouldn't be surprised if someone well trained in stage combat could perform well against the average poorly trained swordsman.
Olympic fencing has very well-defined rules, and so is a poor reflection of actual combat. You can lose a point in fencing just because it wasn't your turn to attack.
Kendo is highly ritualised, and therefore has the same problems. The shinai (bamboo swords) also behave very differently to actual swords.
I forgot to mention bohurt/buhurt, which, as far as I can tell, is just Eastern European chaps donning plate armour and giving each other concussions with pollaxes.
Kendo and Fencing are both sports. For starters a shinai is way lighter than a real sword, even an iaito is usually lighter than a real sword. The "meta" then evolves around a might faster and lighter style.
Slicing with a katana is also very technical, if you've ever watched tameshigiri being able to properly cut is much more than just scoring a point. Kendo tries to simulate that in its subjective judging parameters, but having your attacks properly cut will be a different technique than sport Kendo.
In real life warfare knowing how to not get your weapon jammed in an opponent is important for survival but is very hard to practice in modern day life...
Edit: as an analogue: if you learn boxing or muay thai, first you learn how to hit a bag properly. Then you spend 10-100x longer figuring out how to execute those techniques in an actual fight. Then you watch a master like Canelo or Tawanchai work their beautiful art and feel depressed
Kenjutsu is the older Japanese martial art of fighting with a sword and has a wider selection of techniques, but isn't a sport. Some of the schools do spar, and the end result doesn't look quite like kendo.
I think the biggest difference between HEMA and modern (sparring) kenjutsu is the weapons they practice with, their weight, shape, length and style of use -- matching the random path of history in each region.
Olympic fencing obviously sacrifices something, but as a layman I'd have trouble describing it.
Kendo uses wooden swords, does it sacrifice anything else? Would practitioners be proficient in HEMA and vice versa?
Another widely practiced sword art is stage combat. Obviously it has a different focus, but I wouldn't be surprised if someone well trained in stage combat could perform well against the average poorly trained swordsman.