My memory is that CO's outfit designer is stuck behind a massive amount of lockbox unlocks (which would be my gripe about STO, as well.)
Not really. Most of the good costume parts are from other sources than lockboxes. Mostly events. Back when events were much much fewer and far between that was a different case. But between when I stopped playing CO and when got back in it has shifted.
That can of course change if a lockbox had some interesting pieces. But in the last 3 years its been rather meh. And often anything you might want from one ends up in the exchange at sometimes reasonable prices even.
Currently the sources of costume parts on CO are...
Drops: I never seem to have any luck with costume drops. But one of my friends has had pretty good luck there.
Events: usually at least 1 new piece every event. Sometimes 3 or more.
Recognition vendors: Theres several now and some are easier to get points for than others.
Costume Contest tokens: Never won one. But at the end of every contest is a battle and award of a basic dev token for a hidden shop.
Trade Paperback shop: This comes around every few months. Ive never had any luck with the higher end vouchers. But not bad with the commons and so on.
Voucher vendor: Costume vouchers go on sake in exchange often really cheap so it can be a good way to get some parts without resorting to lockboxes. I tend to buy a few when they are cheap and hand off to friends who are just getting into CO.
Lockboxes: In the last 2 years alone the costumes from lockboxes has been rather bland. Attention seems to be more on the sidekicks from those. Keys can be bought off exchange if course rather than with zen.
All this is VERY YMMV as what I consider good or not someone else might feel the opposite.
As for STO... Lockboxes have costume parts? When? I've never seen a single one in a lockbox loadout so far? I'll have to recheck but pretty sure no recent one has had any.
Now lobi shop costumes is a different matter. Unless are playing the long game for the yearly lobi haul option, lockboxes are the only way to get crystals. The rest are locked off in the Zen store. Though you can just trade dilithium for zen and go that route.
STO feels the most anemic and limited for costume parts of the three. Seems more than a few sets can not be mixed with other sets. Especially the rep unlocks.