Since there is rarely anyone on perris anymore and thats where most of the benefits are, I think SBI should be available to diamond package aswell. You only get access to the harbor department which in my opinion, is very boring. And the other benefits are just some exp and cash bonuses.

This will not happen, as it will make the game pay-to-win. There is already enough SBI, and having it locked to the highest tier ensures competent individuals enter the team. This also ensures that there's chances for non-donators to go on the SBI team, otherwise everything will be full of these pay-to-win donators.
I get that you feel like PAPD is boring, than it is just not for you and you don't know how to correctly utilize this team. Port is a location for drug dealing and you are supposed to patrol it, you just sit at a gate, that is why it's boring, because that's all you might be doing.. :D

Even then i've been trying to get onto the police team to maybe grind for it but in every single server the slots are full for hours on end.

isnt it enough that the ultra mega losers with founders edition get SBI?