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This is just a thought, but maybe one of the reasons why these "optimal builds" are so much more effective rather than being flexible and allowing for more verity for player developed sub classes of the mechs, is because the tuning options are directly connected to the mech's key stats such as armor, hydraulics, weapon's loader, etc. Meaning that the current turning system can negate many of drawbacks that are built into a class by design.
Maybe if tuning effected some flat arbitrary, universal or unique, aspect of the mech, that was more of a side grade function rather than an upgrade, maybe tuning could be reintroduced in a different way. Kind of like how a driver can tune a car so the gas, brake, steering, mirrors, and so on feel just right for them and them alone (I know there are deeper things that get tuned but I don't feel like looking them up). Or how a gunman tweaks the trigger or can swap it out for something lighter or heavier. Although these might be extremely bad examples.
Spoiler
In general models of a particular machine are all the same, but when you get a machine you like to tweak how it feels so it is most comfortable to you (much like changing the mouse sensitivity). If those elements could be isolated and applied to mechs individually maybe that is what tuning could be. Not about performance but about feeling of control.
Anyway, that is my random thought.