sure it is the best opening but nobody figured it out at top level!
E4, E5, the king's gambit, is it the best opening?

Absolutely it's the best. It's scary to play as white and scary to play as black. What more could yo ask for? At least you don't have to study endgames, so it has that going for it.
OK, that part about endgames is not true. When you play it positionally.
sure it is the best opening but nobody figured it out at top level!
You don't "figure out" what is the best opening, you have an opinion on it. The King's Gambit flourished at the pinnacle of chess for hundreds of years and it continues to do so at club level and non-professional.
The strength and knowledge of the opponent matters. The elite probably can't play it regularly nowadays due to encyclopedic opening knowledge and unfathomable technique and calculation ability to work out the problems white sets for black. The rest of us mere mortals have no business doubting the opening's chances unless black is at least GM level. I think high-rated computers (3200+) often prefer openings like the London System to the queen's gambit. Does that mean the London System is better? No, but it's likely safer than the already safe queen's gambit. However the queen's gambit is still incredibly effective against other humans, so I doubt any super gm would consider the London System as the best opening, because it is neither effective or very interesting against other humans.

I feel like it is because you activate your bishop and queen, and usually you'll attack with a knight or defend with a knight/pawn/queen.
You don't need to play the king's gambit for that.

If you play it as white or black (but specially as white), be prepared for complicated positions where daring and creativity (and calculation) matters more than material. Not a lot of end game studies here as games don't usually last that long 😂 an opening for chess romantics!

If you play it as white or black (but specially as white), be prepared for complicated positions where daring and creativity (and calculation) matters more than material. Not a lot of end game studies here as games don't usually last that long 😂 an opening for chess romantics!
Agreed.

2...Qh4+?! 3.g3 Qe7 (with a slightly better position for White; at the cost of being put in an unfamiliar position.)
The few times that I played 2...PxP, I was cut to pieces, even by lower-rated players. The lines can become extremely complicated, and White can obtain a decisive attack if you make just one mistake.
I feel like it is because you activate your bishop and queen, and usually you'll attack with a knight or defend with a knight/pawn/queen.