Im kinda really recommending the adding of new additional servers. And free server transfers at this point.

1. Additional Servers that Legacy players may transfer if they would like.
2. Additional servers that anyone may transfer too.
3. Prevent further non-legacy players from creating characters on legacy servers until a population hits near a certain quota of players.

Alternatively id say just enhance the strength of the servers as much as you can then reduce it over time.

Additionally you could open up a ton more servers -

in the future...
add a cross server playing thing where player can play PVE content cross server open world without the server being a total brick wall. Or something like that.

Its pretty frustrating having to sit back hearing your friends play the game without you. Getting errors when attempting to login.