I wonder what is more effective in a war when you deal with opponents you cannot break. And you deal with a province with high wpa and tpa so other methods of decreasing defense do not work.

Say the opponent has 100k defense
All attackers have 80k offense
Is it more effective to send 16 gens with 5k or let 1 person conquest with 80k offense?

What method kills more defense? And do you have relatively more deaths with bounces or conquests?
Can you plague someone with bounces or conquests?
Do both methods increase GBP?