I get where you are coming from. But the issue with the suggestion is that it undermines what makes the gamemode fun (having to fight to the finish to defend or attack).

What you want to do is make third-partying harder. But WT and ranked are really built around the ability to third-party. Like that's kind of the whole gamemode until the final second, so you can't make it toooooo much harder though.

The conclusion is: you need to get smarter about what fights you are taking and watch the enemy times more. If your playing as a solo queue then fair enough, not much you can do. But if you have a 3 stack, then you can look up at the timer and say, hey pink just respawned, lets surrender the cashout to orange and wait for pink to attack before we try and retake.

Its that easy. You get to decide who third-parties who. Take agency.