I can't count how many matches I've played where the other team switched load outs because of losing. It gets annoying and shouldn't (according to history of trials modes) be a thing. If you are one of those players, you should stop doing it and stick with what you go in with in order to prepare yourself.
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Trials should have locked Loadouts. If it doesn't however you'd have to be stupid to not adjust your loadout to better combat the enemy team. If you're legitimately upset that the enemy team doesn't stick to a losing strategy you've got some serious butthurt.