That is a terrible idea. The system prior to 1.5 worked. You had a one minute window to join which meant that your group could get in from open sea if you had to chase someone down (separating the fast and slow ships open world).
A better compromise. Make a 30 second window after the tag, allowing all to get in initial fight (it is unrealistic to expect a hunting group of a variety of ships, especially different class ships, to maintain cohesion especially when chasing someone down). The next 30 seconds the battle is still open, but anyone joining spawns at a distance behind their side's starting point.
Mechanically limiting forces is bad. Fair PvP options are there, open world should be risky and it should reward the players that organize. We have already lost players from my group that were locked out of battles and saw no interest in sailing around open world for the odd fight and then missing out.