Whilst it's true that this is a VIP feature that people have paid or donated for this whole issue is ruining the server drastically...
Here's how it is: If a VIP would want to join a class they would want to - they most definitely can - all the time. The new balance update doesn't change anything, you can easily bypass the system balance with a reclass to the opposite team of your preference and then it would allow you to reclass to the team you had initially wanted to be in - yes, many VIPs do this which simply puts the new update of the balance system to no use.
In my opinion, the ability to choose whatever team you want as a VIP is really having a negative impact to the server, it's worse than the whole chainsaw and sniper issue we used to have. Newbies, Non - VIPs, players that just aren't friends with the server friendship group and even regular VIPs who want to enjoy the game-mode sometimes or usually have a rather disappointing or negative experience. Here are a few examples of what happens on a daily basis throughout Plan B: Presidents either have A LOT of security or they don't have any "strong" or a small amount of security to their aid. The well-known VIPs would be able to attain a huge mass of security since most of their friends would be able to choose whatever class they want (most of the people that have friends in this server are VIP anyway). Situations like these cause such imbalance like the one MegaPilot has shown. The other one - an unseen newbie that wants to try out the server becomes a president since they saw it available and that's what pops up first. Little would he know that he had no chance to survive. The whole VIP squad (excluding the minority that does want to balance the game) would go terrorist without considering how weak the opposite side is then gain a lot of president kills, change the map within 2-3 minutes and then leave or rest as a civilian. Another casual scenario, when they are the only terrorist/cop trying to play the game-mode and a few VIPs that have gathered in the opposite team chase them for fun ruining their chance of fun, repeatedly dying. We already know many more instances where it makes it un-enjoyable to play, those were just the basic scenarios that happen all the time...
These regulars would always be here or would play at the server for quite a long time however those newbies that had high expectations of the game-mode wouldn't return. We can see this by having peaks of 40 players at certain times. I don't see most of those names again. I believe this is what causes our server player base to always remain the same expecting 18-26 people a day, dependant on the regulars to play.
What I believe would happen if this is changed: newbies and non VIPs would be willing to be regulars which is always great. They would want to stay as they aren't being chased by an imbalanced herd of security when they are trying to kill the president or an imbalanced herd of terrorists when they are president. The VIPs would then either be in classes where there's a balance in power or doing their usual civilian job. There's definitely room for improvement with the civilian issue but there's already a suggestion topic about that so let us leave it there.
My own small input to this would be to reduce this VIP feature from 75% to somewhere around 55- 65%. As I'd said the current 75% is meaningless it's the same practically. The reason being for still siding this to be a VIP feature isn't because I have paid for VIP, it's because there are some VIPs that care about the balance and they would reclass to balance the power when the aforementioned scenarios happen.