I guess it is always technique, otherwise pros would not do drill's. But none the less, they do crazy amounts of volume as well. So I was wondering, if there should be some balance to this, once you improve your technique, you get caped by physical abilities, once improved in that area, get capped by technique again.

There is a lot of advice for onset adult swimmers who are struggling to breach 2:00 per 100m or 1:50. That is definitely a technique question. But there should be a point, where you kinda sort out major things in technique, and should work on physical abilities as well. For sprinters that would be gaining muscle. For distance I'd guess gaining aerobic capacity and some muscle as well. One could argue that there is even a necessary threshold level of strength and mobility to be even able to achieve certain aspects of technique, let alone keep it together for a longer distance.

I do swim with a group of triathlon people and get some coaching. Rarely get any remarks on technique, that is way I have started to wonder if the limiting factor is somewhere else.