The cost of units doesnt scale with the amount of metal you can have in storage, thats true. You can begin building a Starlight in the first second of the game.
However, early game (when u have low storage), having enough metal to boost a LLT can make a impact.
As the game progresses and your economy scales your storage cap (usually) increases - and by then having enough metal to boost a LLT will mostly be irrelevant.
You can set your storage level higher from the beginning, but then you are going to screw over ur early game by always having a couple raiders less than your opponent.
Also, ofc you can manually adjust your metal reserve over the course of the game... but damn, thats cumbersome.
Probably not worth the effort except for some super-rare cases.
But as a few seem to be happy with the fixed reserve level, how about just adding the option to have a scaling inital metal reserve?
So there would be 3 options:
[ ] No metal reserve
[ ] Non-scaling metal reserve (amount: ___) (aka: What metal storage currently is)
[ ] Scaling metal reserve (Enter % of total storage capacity)