So...monsters get an additional attack every 5HD or so.

So...monsters get an additional attack every 5HD or so. PCs don't. Their stats go up, but generally those have a capped effect on AV and DMG.

So...won't this lead to drawn out, HP sponge combat at higher levels? Shouldn't PCs have higher damage at higher levels, or multiple attacks, or something?

Or are we relying on magic items and such to increase their damage?