Why can't i use this to route packets dport=995 off the VPN?

First add an iptables rule to mark specific packets:

iptables -t mangle -A PREROUTING -p tcp --dport 995 -j MARK --set-mark 0x200
iptables -t mangle -A PREROUTING -p udp --dport 995 -j MARK --set-mark 0x200

Then add a policy routing rule that matches the mark:

ip rule add fwmark 0x200 lookup main

There are other possible combinations – for example, mark all packets meant for VPN (making the existing from rule...​