Ancalagon
Dusty Dragon
Being someone who is concerned with fairness - or at least likes to think I am - I will now disagree with my previous reply, which was aimed at the OP's claim that 5e wasn't combat as a sport.Combat as a sport is never "roughly equal" because if it was, the PCs would lose frequently! Instead it creates the illusion of being a roughly matched context - but it is that, an illusion. In almost all fights the PCs are almost guaranteed to win... which is why the PCs are going along with it. If the 2 sides were roughly equal, the players - after losing a number of times - would try to tip the scale in their favor via various shenanigans and cunning plan, moving towards combat as war.
So I disagree with you - 5e totally is combat as a sport. But it doesn't have to be.
I think that the main determining factor is not the system, but the players and especially the GM.
First, one can do combat as war or as sport with any system. In fact, I think that rulesets with more complex and "tactical" gameplay are better for combat as sport, because the fight itself is the action - there are all sorts of things and powers and cool stuff the PCs could do in the big battle vs the BBEG in their throne room. And the GM may spend considerable time thinking about this big showdown, placing hidden crossbowmen on the balcony above, maybe a magical field protecting the throne etc etc etc.
If the PC plan on climbing the walls of the castle and murdering the BBEG in their sleep, (or any other "outside the box" thinking that will crush the opposition), combat is almost a foregone conclusion - there is no "need" for a full, complex combat system, since the real "action" wasn't the fight, it was the scheming.
Because the DM has to react on the fly to the PC's plans, it requires good improvisation skills, and a high level of fairness - would the foes have thought of this too? Perhaps the BBEG has powerful wards protecting their bedroom window for example. It also requires a willingness to "let go" of plans (that big set battle may not happen at all) and also a willingness to sacrifice "a good story".
I remember an encounter vs some kind of large, cursed boar (this was PF1e, Kingmaker adventure). Our party devised a cunning plan that basically involved a magically sped up PC provoking the boar, running away and drawing it into a heavily trapped ambush area. And it worked like a charm, we obliterated that boar.
But the GM wasn't happy. Even though the players had had a good time* , he felt that it should have been some big epic battle and that the encounter had been ruined. So our capacity to "game" the encounters grew less and less, with encounters starting more abruptly.
* why did I add the star? because there is a caveat. Looking back, I'm not sure if every players had a good time! Combat at war relies a lot on planning, and if some players don't enjoy planning, they won't have fun!