Team-switched or not, no one should be spawning at these locations at the start of a round. Let's say attackers got a tent inside a hidden nook that's near a gate they can open quickly, sure if they get team-switched they shouldn't spawn there anymore, but neither should the attackers still on offense at the start of a round. Everyone should spawn at the regular starting spawn points, not get an advantage that persists through rounds.
This isn't about a strategy that's over-powered or new, it's about a strategy that creates an obvious abusive situation when things go right. Just because someone finds something that can be abused, doesn't mean they should be using it. Like when pikes and long spears weren't to be used on horseback, or the siege construction piles when they were indestructible. It wasn't a matter of being an over-powered strategy, but because they weren't working as intended.
Now, if the powers that be wish to rule that using spawn tents in their current state, that can lead to people spawning at the start of a round that bypasses defenses is fine and dandy, then I propose making doors and gates remain in their same conditions at the start of a new round. I mean, it would be just good strategy to go around breaking all the doors in the first round when they're weak so that you can have an easy path on the following rounds... and if the defenders can't counter that, well too bad, yes?