Weight is usually a feature for locomotives, which are sometimes ballasted for extra traction.

Occasionally you see extra-lightweight engines designed for light infrastructure-- often putting the same guts on more axles to lower the load, but it's rare.

Modern locomotives also use AC traction motors, with sophisticated computer controls to generate an AC product suitable for the desired speed and torque. Even modern diesel-electric designs have alternators and AC internals. Yes, some old electric engines were huge rectifiers on wheels, but that's no longer necessary.

Electrification is a very "capitalism won't let us have nice things" problem; it's a 25 year commitment to infrastructure and new engines before it pays full benefits (higher reliability, simpler equipment, higher horsepower per unit, using dynamic braking to return power to the grid)