Remove HP trinkets, and UVs.
You want to play striker? Fine but you have to deal with getting killed easy.
Recon? You won't be able to use a sword as well, or move as fast, unless of course you are willing to sacrifice damage in order to use ASI/MSI boosting armor.
Guardian? You have HP but your teammates will often run off without you, plus you can't gun as fast.
Give players the option to vote for maps and AT toggle.
Divide teams based on their average loadout power (excludes loadouts that could be used in tiers not applicable to the current tier).
Want to play old LD? Fine but you can't get on the leaderboard anymore from there.
Creating balanced lockdown threads don't usually get far unless you're putting a band-aid on the current system. Removing things isn't the solution always, adding things would. Right now, players prioritize certain gears because of the bonuses they get. With trinkets, they optimize their playstyle, plus trinket slots don't cost all that much in the long run.
Lockdown cannot be balanced with all current game mechanics in place. Server delays will cause issues. Gear choice will not change. If you were on the testing server for the gunner update for Lockdown, where players didn't have their amazing gear, the game was sort of balanced. No health trinkets were a part of this, and they couldn't just use full chaos armor and have max ASI anymore. It was fun, but it would also get sort of bland in all honesty.
My own suggestion is to make more gears viable in lockdown. Right now you rarely will see a player in any angelic or drake scale line. Salamander is unheard of. I believe that making family bonuses (Fiend/Beast = striker, slime/gremlin = recon, undead/construct = guardian) would make many other lines suddenly become really viable. Arcane Salamander would see some use as you get bonus damage vs strikers and recons plus great elemental/normal defense, on top of fire resistance. Valkyrie would be great for recons who want to prioritize strikers. Argent peacemaker would be extra effective through a guardian's defense. Heck, all the status shard bombs would become more useful as area of denial weapons, and this would also make rolling fiend VH on a weapon desirable alongside that ASI. This also creates a larger UV market for PvP players, and makes more advanced gear tactics for older players. Mix black kat cowl with valkyrie to negate the curse vulnerability and get ultra damage VS strikers, or mix arcane salamander with chaos and get extra defense and fire resistance while still dealing high damage to strikers and recons.