You actually can have two problems with your character being heavy and if your map were more vertical, the first is that it would be a hassle to navigate, since you would have to jump a lot, and it would be pretty easy to mistime your jump because of that. The second one is that, if you fall, and your character being so fast while doing so, could cause the character to get stuck between collisions while the frame is updating, and constant collision check would have an impact on performance.
I realized you could hold the jump and jump higher, but some people might not, they might be new to platformers, so it's good to inform them of that in the tutorial.
Like I said, the issue with you current attack speed is just that if you plan to add a fast enemy the player would have to time it VERY well, or just tank a hit, I actually thought it was pretty easy overall, I just had to stand still and smack the s*** out of the bosses and enemies, as the attack collider was very big, considering the animation. And YES that jump attack, I really missed it in the game. But I really enjoyed it a lot, it was very fun and I would love to see your game finished