1st point: No, equal skill means your counter-snipers will nullify the effectiveness of their snipers - either by killing them while they're acting as snipers instead of counter-snipers, or by forcing them to play counter-sniper and ignore the targets they'd normally go for. Either possibility means their snipers aren't doing the job of killing the guys who are advancing.
Equal skill means, that their snipers have a huge advantage given by the map. Hence why your snipers have a much harder time to spot and eliminate them. There are
about 5 positions where Resistance snipers can be. There are
exactly 2 positions where Security snipers can be.
And Resistance can always use the height advantage.
2nd point: You don't have to spawn-trap them, they can be allowed to exit the spawn at the further exit from the bot, and retreat away from it, as long as you demolish anyone who doesn't fall back on the way out.
Well, yes and no.
You can - basicly - let them exit their spawn on one side. But they will just end up entering your line of fire while you're guarding the bot. And you wouldn't simply let them pass to allow a flanking maneuver, would you?