Rizzler if it really bothers you, depending on what VPN provider you use, you can download an OpenVPN config and use the OpenVPN app.
All VPN providers I have tried, don't bother attempting to limit consecutive OpenVPN connections (at least, not when made in the way described above). It's probably more work than it's worth, I imagine.
I'm not vouching for the speed or the security etc, of this method though. In fact I'm pretty sure the only VPN app advised by GrapheneOS is the Official WireGuard app.
I guess another method could be to use your home router, if it has the functionality. When at home, you could leave all the VPN slots without a VPN and connect your router to a VPN via a downloaded WireGuard config. Then when not at home, you could set up a VPN server on your router and make separate configs for each profile etc etc, I think you get the point by now...
Personally, I like having separate VPN slots for each profile as it helps with keeping them isolated.
@Rizzler mind me asking what VPN you use? Or how much it costs per month?
Edit: Actually, maybe leave it as I'm just going to derail the thread more with stuff that isn't really relevant to the topic. The reason I asked is because I find it hard to believe it could end up costing you that much extra by taking up a couple extra VPN slots