One solution would be to have the players have a primary and secondary character.
So the player who wants to have the tech as their primary character, has that, but for combat focused scenarios either plays a secondary combat character, or helps the gm play the opposition forces.
And vice versa
That was actually what they suggested in the very first edition of Mechwarrior. I'd actually go further and do something like Ars Magica's covenants. Everybody does a primary and secondary character - get them to be in different spheres - and then create a supply of quick and generic extras: Astechs, Infantry privates, reserve pilots etc. Then, if the Chief Tech and the techwiz are working to fix the Dropship engine in time to take off before the Fedrat scum arrive to blow your mercs away, the other two players get to play the extras for a bit (probably an Astech or dropper crew). Likewise, if your 'Mech lance is in a running battle, have the tehcwiz player run the vehicle commander.
Now, I have no idea how complex the character creation rules are for Destiny (I didn't Kickstart the Clan box), but maybe this needs there to be a simplified version for doing the extras? Might be useful as an optional rule.
Actually, isn't this what Star Trek Adventures does as well? And 2e Werewolf: Forsaken.