Chaos structures.

not Hydras, but the army as a whole... why doesn't this apply to Percy and bots???
what "gap in turns" are you talking about?
a hero's army + Chariot of the Dead has exactly 30 turns without artifacts and abilities, I repeat, artifacts and abilities increase the movement of the hero AND HIS ARMY on the map.

The point is that overall. Or is it not obvious that armies with Chariot of the Dead accelerate better with percentage bonuses? ;)
Okay, fine. I'll break down the math if you need to.
Army with Chariot of the Dead (hereinafter AЧД) = 30
Army with Hydras (hereinafter AГ) = 22

So. We add a standard speed booster and gloves – +50% +25%. The speed booster is always present, and gloves are almost always available on online maps. We add a cart = +7.
I specifically don't add an oasis, stable, boots, and the Endurance spell to maintain an average. Otherwise, the gap will be even bigger. Let's see what we get:

AЧД = (30+7 – base turn with a cart) + (30+7)*0.75 – bonus from the speed booster and gloves.
AГ = (22+7 – base turn with a cart) + (22+7)*0.75 – bonus from the speed booster and gloves.

We use a calculator and get the numbers:
AЧД = 64.75
AГ = 50.75

Is a difference of 14 squares per day small? It's more than half of the hero's base turn at the start. Use Hydras for their health, for goodness sake, if turn count isn't important ;)