The game pushes you toward speed.

[MasterWaffle]

The spider, and two bosses gimmick is to beat there speed. Early game you are pushed toward speed builds. Also I find the only way to effectively beat the 3rd boss consistently is to use speed builds, like the rapier+ yellow crown + leather set/other speed items.

Trying to do Hp, shield, thorns, will often get you killed even before the 3rd boss.

[Fool]

Regen (armour or health or both) builds work really well against the final boss (maybe best).
As does armour + huge attack strength (or multi-attack as you mentioned).

I just won with a thorns build, but it relied on two items only unlocked through challenges so doesn't help the early game variety.

[Brenus]

Disagree, fire bro can can get rekt with a firecracker and the 1/2 damage charm, spider you only need a few points in armor and a half decent weapon, The Boar is he only one where speed is almost a must but i've taken him down with an armor and regen build but yeah he is still a bastard