Currently WMMLP: considering W vs Pal & L vs 3rd M

[nodoze]

What you have should be workable and I would try every recommendation before leveling up alts.

If you do find nothing works for you having at least 1 Paladin in the party (either the healer or the Tank) helps make aggro much more manageable though personally I don't recommend a single Paladin healer if your party is all melee (except maybe at cap with great gear on your melee for PVE). Your party is ranged so not a concern but I just wanted to denote that caveat for melee groups so that other readers running melee don't think I mean that in all circumstances...

Personally I think Paladin is the best/easiest Tank for reasonable pulls for dungeon clearing via built in tools for most people (especially on a new team and/or a team without a Paladin healer). Having cleanse, self/off-heals, bubbles, auras, buffs and a 2nd Rezzer is a lot of value in addition to threat management (not all parties need salvation). A Paladin Tank can also turn a single healer team into dual Healer team for WPVP which really helps WPVP viability for many teams.

A Lock's utility is more than just summons as should be able to use 'eye of kilrogg' for pulling, give rez stone, health stones, party/tank buff (or offtank pet), among other things and post 30 a Lock's AoE should be close to a Mages. It is up to you but some folk even do all locks or only 1 mage so any/all options are viable and they are essentially interchangeable with pros/cons. Personally I think having at least 1 of each gives the best party synergy (unless you already have a Mage at cap to give your party free water and then maybe go all Warlocks).

If you do level up a duo to swap and contrast/compare based on your concerns I would indeed do a Paladin & a Mage but, since you have a ranged party and already have a Warrior, actually I would try the Paladin as the Healer with your Warrior Tanking just to see if it suits you better before abandoning the Warrior... A Warrior with Retribution Aura and the rest of the party getting -30% Threat due to 'Blessing of Salvation' may make it to where you really like your warrior and don't have to micro-manage him. If you have had problems with your healer getting aggro you shouldn't with a Paladin as they are at 25% healing Threat to begin with (compared to regular healers being 50%) and with -30% on top of that a Paladin healer should realistically never take aggro. I do like Priest AoE healing in emergencies but if you are tanking effectively at range with good aggro management the Paladin healing should be enough (especially in an all Mage or mostly Mage party where AoEing doesn't cause loss of health).