Might be an Hot Take, But i DON'T Want Full Mech Customization
I'm not saying that i don't want free mechs, that's a whole different topic and not the point i want to make... but yeah, you read that right, i DON'T want mech customization, and that's mostly for balance reasons.
Having mechs presets is much more interesting, because AH can balance them to have specific strengths and weaknesses, meaning that choosing which mech to bring is an interesting decision that changes depending on faction, mission type, constellation, biome and team composition. It encourages teamplay by choosing mechs that cover your team weaknesses, like needing more long range add clear, or more defense to escort a high value target.
Not having customization means that one mech can't (or shouldn't, balance isn't always perfect) be strictly better than the rest. You want an AT weapon? You will only get one then, and the other arm is a flamethrower, not something comfortable like a minigun or long range like an autocannon. You want a shield? Sure, but you'll have to use a shotgun, no long range weaponry! Want rockets? Why not, but you'll have to use a minigun, not something even more AT like a cannon.
These presets force the player to make decision, instead of crafting their perfect one-size-fits-all solution to everything. It also allows AH to make these choices stronger without breaking the mech balance. It would be fine if the Bulkward shield was invulnerable like devastator ones, after all you can't pair it with a true AT option, you're stuck with a shotgun, and you'll have to deal with it.
It would also probably end up being filled with useless filler options just for the sake of it. Different armors, different legs, maybe accessories like stratagem thrower and portable shield... but we all know most of them wouldn't be used, just like everyone uses vertical foregrip on 90% of weapons. Just slap on the chassis with the highest defense (if it allows to tank more hits, otherwise the one with the fastest speed), fastest legs, stratagem thrower, double AT cannons, and you have everything you'll ever need...booooooring!
I don't need everything to be 200% under my control, fully customizable with dozens of options. Sometimes, fewer more thought-up choices can be better than hundreds of bland options, with a few clearly better than the rest.