So let me try and make what I personally believe to be a stronger statement as to why to get rid of plex for game time, because it would make CCP make slightly more money. That’s about all it would really do as a benefit. All of the people who have stocked up on plex would suddenly get rid of a good portion of it because they wouldn’t be able to use it for game time so then they would buy skins and extractors and such so that they could make money.
Multiboxing isn’t being caused because of plex being used for gametime. Multiboxing is due to a lot of factors such as players wanting to have the upper hand on others because you have more tools at your disposal, or being able to move your own caps without relying on others who you may or may not trust. There’s a looooong list of reasons Multiboxing is a thing, in fact I have 4 Omega accounts and 1 Alpha. I use the 4 Omega accounts for nearly everything. I have yet to actually purchase game time with Plex.
Now as far as the null sec dynamic goes, that’s up to the kings/queens of null sec and the ceo’s that people follow to create a way of protecting ratters. OR ratters can work together to kick ppl’s butts… Ok, someone just snickered in the back of the room, lemme explain. Let’s say you and one other person are in a belt mining away. You get jumped, you are probably going to lose because there are 2 of you. However, lets say everyone in the region mined in one belt/system and then moved as a fleet. Say you have 15 mining barges. Put some tank on those, Put a DDA in the low slot, suddenly whatever dps you have is multiplied by 15… that’s a lot of damage for just a mining fleet. Suddenly that small gang that was going to attack, just lost all their tackle ships because you shredded them apart. Suddenly their bigger ships are questioning if they reeeeaaaaally wanna give it a go.
TL;DR: You’ve stated, I believe incorrectly about how there’s a problem and this other thing that has very little to do with it is the cause. And they design this game so that no matter what, having larger numbers means you are winning.