I'm pretty sure I read an article or something by an actual swordmaster who said that fight in ANH is the closest to a real sword fight (between two people that actually know what they're doing) that any of the OT Star Wars movies got. ESB was a very close second IIRC, though it was specifically designed to show Luke was inexperienced; incorrect stances, angling the blade to high as he advances etc.
Apparently all that flashy exaggerated stuff is mostly just theatrical sword fighting, whereas the real thing (where you legit will get the top of your head cleaved off if you loose) is about stillness and an economy of movement. Concerving your energy and doing only exactly what you need to do and no more. Even the weird little blade twisles that Guiness does is supposedly a thing you would actually do. It doesn't look impressive, but it's about feints and controlling the position of the opponent's blade. So with all that in mind, I totally buy that this was a fight between two Masters 100% ready to kill the other or die trying.
Indeed, we even see this again in Rebels with Obi-Wan & Maul. It's over in seconds with the absolute minimum of movement.
With their last fight, Anakin on the other hand was dead set on murder but Obi-Wan wasn't ready to take it that far. Even right until the end when he gave him a chance to surrender...and even after he dismembered him he couldn't being himself to make the killing blow, which he'd no doubt regret later. Hence how elaborate and drawn out the whole thing was, because one opponent was playing mostly defensively.