Large mining machinery (Haulpaks) are the same - electric with a diesel power plant.

I don't believe the wheel weight is a big issue in these cases - particularly for the AC systems, which are somewhat simpler and more robust (in terms of the wheel motor, the actual control system is much more complex).

The reason they use an electric system for Haulpaks is varied - but basically it's due to the fact that a mechanical drive system is almost infeasible at that size/load/torque. An electric transmission system is easier to control and more robust.

Also, electric lets you control the torque much better, particularly in the AC case where they can adjust phase/freq/etc to keep it controlled.