As mentioned before - mechanist should be given his tool belt back when no mech active - giving it away is a bit too much for 100s cooldown. And there are a lot of skills on tool belt that are essential to engie gameplay (like bandage self, and most of the stun breaks are on toolbelt).
2nd of all, this cd is just enormous.. mechanist is an engie with a pet, industrial version of a ranger, but ranger gets 60s cooldown on his pet dying, and always has the second one to swap to. Mechanist on the other hand is half the core engie on mech dying.
And one another thing - do not send back the mech when mounting up! It goes on a 10s cd whenever you mount (given he's full health) which is just plain annoying. Rangers always have their pet active. The moment they dismount, it's up.