After some long experience in l2 interlude i have to say and suggest the following about class balance on server.
Hawkeye - completely useless since dash has soooo long cd. The advantage of the class its its speed comparing to other archers and in this server one has to sacrifice 3 buff slots in order to get it working on good cool down . Thats the reason no1 plays it and the only archer class worth making is GS. Please consider fixing that in next season if you want to have more diversion. ( i wont say much about elf since the low range makes it bad anyways )
Ghost hunters : huge damage comparing to human - elves daggers. I would recommend to Nerf it a little bit.
Gladiator's : Huge damage of TT''s Critical , can one shot almost any robe in Oly. I would recommend to reduce that a bit.
Overlord's : Its a shame to not get heal , res or even cleanse by BP. A single Warlord has higher sustain in battles than the OL and still can get heals res etc. Tested that alot since i played both alot. I would recommend to change that next season.
Mages : Haven't tried mages alot here but noticed Spell Singers do not have the higher magic critical rate as it should be SPS>Sorc>Necro=Sph. Wild magic augment is not working good and SPh's have more m's rate than normal.
Sws / bd - I did not play the class but i would recommend to increase the chance of medusa and song of silence and make them more tanky in order to motivate ppl playing them as CC roles for more diversion.
About party set up.
I would recommend to increase the party size to 6 ppl.
Enable set ups like 1) BP / OL 2) BP / EE -- 3) 2x EE - 4) 2x OL - 5) EE / OL.
Yes there is gonna be more heal but more DMG as well so there will be balance and more diversion in parties.