If you're playing Domination, you should never triple cap in the first place.
By holding two of 3 flags, usually A and B or C and B together, you already know where the enemy team will be spawning, so you can better defend against them depending on the map.
You can also unload your killstreaks in their owned flag to usually hit at least two enemy players, if you wish to do so. Capping all 3 flags in domination is just pointless unless you absolutely need to lockdown the game to win, because it makes it so that you don't know where your enemies are going to spawn from, which is frustrating later on when/if you're building up killstreaks and you lose them because someone randomly spawned behind you.
As for playing with randoms, its possible to do well, its just a lot harder if people do not capture flags. Your team does need to understand that your side needs to maintain control of two flags for most of the match, and needs to cooperate to that extent. Sometimes, if you're really good, you have enough momentum just by racking up kills and killstreaks to swing your entire team into a winning position, but this is less likely when you switch over to Ground War, where people really need to cooperate to get anything done.
The right way to play domination is to hold two points and defend the center (B). While its true that you can lose to enemy players having A and C, because of the spawns, its easier to get those points regardless of the map, whereas B is usually smack in the middle. If your team isn't helping or isn't good, that means its up to you to switch to your flak jacket pro, tac pro, smoke nade class and cap the pivotal point.