What is hard to cross in is that metal halides actually start out at very high efficiencies.
Convert 400 watt metal halide to led.
Commonly a 250watt 400 watt or 1000 watt.
A metal halide light that produces 30 000 lumens discharges 75 lumens per watt.
Many of the concepts are the same but there are some differences between 400w and 1000w metal halide.
Most large fixtures use metal halide bulbs.
The reality is that they come in a large variety of options.
The only viable solution currently is to have a module that is matched in size and weight as mentioned but then also has optimised light output to compare with the metal.
If the initial lumens produced by each 400w metal halide fixture were 30 000 you should get led fixtures that produce 30 000 lumens.