STACKING of queues, WAS THE CAUSE.... and you know it. Leaving because a queue popped was an allowed behavior due to the cause. So stop pretending otherwise. In a mature player base where people would respect the group they were in and not jump to a queue pop.... there would be no problem. But it's clearly not a mature player base, it's largely selfish and self-interested... so they stack and jump.
If you want to make JUMP the issue, that is fine... but they can't jump if they can't STACK. So STACKING is the root cause that is actionable by the game developers.
People leave a warzone because there is a scarcity problem. It can take a DPS hours to get a GF queue, and under the old system, minutes to get a warzone (which backfilled pretty quickly), though that could be optimized by reducing loading times, time to accept the invite, cinematics.
People wanting to experience both aspects of the game in a reasonable period of time is not a problem, it's a strength.