That's by design, I think, as there are upgrades to the Combo that activate buffs for 10 seconds, like +10% damage dealt or -10% damage taken for 10 seconds after activating combo.

Also: The description of Dash Combo explicitly states: "Must timeout before triggering again".

it'd be so busted if it didn't have to timeout
even with the required timeout, it's downtime is just like a second to dash 3 times
good for skipping through enemies
great in boss fights, cuz you can't really proc it with other methods (few exceptions)

i use it with every class except for tyrant warrior
cuz you can't dash while you're spinning (whirlwind)

It's kind of a shame we don't have the "Crits give Combo" drink from the first game, but I can understand them wanting to go down a different path with it in this one.