Only because it was DLC added in later. I would assure it wouldn't be if the vehicle was in from the start.
Anyway, I didn't mind the MAKO sequences from ME1 (bar the final one, where it drove on ice. But that was removed after reloading, so I am not sure if that was intentional at all). I didn't mind the MAKO at all actually, not sure where all the complains came from.
Especially if the "fix" is mining and the hammerhead.
Not really. The cannon can quickly make work of pretty much any opponent. And the machinegun you have to aim. Both also have the limited angle, so attacking a camp in the mountains is made more difficult due to positioning. And once you fire, I usually had enemies return fire, or move in my position in order to do so if out of range.
In ME2 with the hammerhead you could fire up-side-down rockets to the moon and still hit your target. And like sheep they all awaited their end, even if it took 100 missiles to do so.