[Anyone ever hear of Battletech?]

they would not be able to have nearly as big weapons due to the fact that the recoil would nock them over. they would be very easy to nock over due to and thus disable and would not be able to move as fast. most infantry would be able to blow them apart with a light rocket launcher or recoilless rifle. their high profiles would make them easy targets that could easily be hit with tank fire.

any technology that could be used to over come these deficiencies could be used to make tanks that are even more effective then the mechs.

there is literally no upside to them other than being cool looking.

[Is it time to give interstellar travel a shot?]

ever heard of the orion projected? it's relatively reasonable price wise and could reach a speed of 3.3% of the speed of light in just 10 days. it's been possible since the fifties. there are newer even better and more efficient versions based on the same principle which are not far of from being possible.