In practice though people are almost never fighting close enough to level geometry to escape clean shots, so unless they're in a faster ship, they're dead, and don't even have a chance to fly in a straight line to some power-up
It is indeed true that beginners don't make anywhere near enough use of cover (and even experts can get carried away and drawn into the open at times) but most of the maps do have quite a bit of cover - especially Ice Field and Asteria, so getting into a boring turning fight in the open is a choice that at least one party to it shouldn't have made in the first place.
Stealth, speed and shield boost are pretty good for running away to - and as the powerups are mostly close to cover, this can be done while using cover to assist a retreat. Equally, trying to shoot someone down before they get through the shield boost adds excitement (and lets people get back into the fight a bit quicker if they're shields down/weak after their previous matchup resolved)
Then you need weapons to stop stealth and shield being too effective offensively.
Obviously if you let one person get all the powerups the combination is too much, but in a match with lots of good players that doesn't happen (and picking up weapons can just get you focused and killed before you have much time to use them)
They're also more important for the team version and especially CTF, where timing a run to make use of shield/stealth powerups, or denying them to the opposing flag carrier, can be crucial ... and the initial positioning encourages team matches to start with a rush for the centre, rather than each wing carefully grouping up and trying to sneak up on the other, to get the brawl started early.
Also, what if powerups spawned randomly?
It'd need the power-up markers to be coloured in on the radar so that you could plan ahead a bit without having to spend ages checking the right panel - though that would probably help beginners get used to the map layouts anyway - but sure, that could add a bit of interest as another map parameter. Exceptions, I think:
- cluster compound, which only has one powerup, should have that always be weapons, as that encourages action while the other three encourage caution. It'd actually probably be worse if someone looping powerups uncontested there could get non-weapon powerups as well: at least as it currently is they can be worn down by attrition.
- CTF mode should probably keep fixed powerup locations because the relative positions of the flags and the powerups are important and should stay mirrored.