Also dangerous for crews. Sherman tank crews had a 75% survival rating when their tank got bust. I think the tiger had an 80% death rate or something.

Difficult to make, too heavy to be effective, and iirc yeah, unreliable.

Even up to present day conflict tanks breaking down or getting stuck can be a major loss of armor, especially during prolonged maneuvers.

That's every one of those big German tanks everybody talks about. The ones they started the war with were pretty fine (limited by terrain, though).