Just some of my Suggestions

Paladin is my main Class that I play and I LOVE IT. But i Feel that Paladins Shield Lob can use a rework. Instead of hitting 1 mob have it hit up to 3 mobs which would help with pulling groups of mobs.

I would Love to see more be put into the Holiday events. Maybe a dungeon that has a boss that drops glamour sets such as weapons and armor and maybe a cool mount.
Example of mounts. Reindeer mount from Xmas and Undead skeleton mount from Halloween events. I thin that would be awesome.

I have more but ill just share these 2 for now. :)

The thing is, if you are in a party there is already a mechanic in the game where enemies will link on the first enemy you pull if they are close enough when you do so. GLA/PLD when it was first designed was pretty much meant to be a class that was meant to excel more in one-on-one encounters and thus most of it's abilities are designed accordingly (MRD/WAR being more the class/Job that excels at handling groups of mobs at once).

Besides, Flash is the ability that's meant to be your group-enmity ability, which isn't that hard to use in tandem with Shield Lob (pull the initial enemy in with Shield Lob, then when the stragglers have arrived, spam Flash several times and that should be enough to keep them occupied, cycling through your enmity weaponskill combo to keep that hate up). It's basic GLA/PLD tanking which isn't that hard to do and thus needs no real changes.

As for the seasonal events, the event team is always thinking of new ideas for events and how to run them in new ways - however, given the fact a dungeon requires a lot of coding and testing to implement, it just isn't worth it for something that is only meant to be a short-term event for fun, they'd much rather leave dungeons as content players can access always (and thus dungeons are always part of the main game) - hence why they usually involve participating in open-world FATEs - the FATE system is easier to implement and access. As for mounts, the recent Halloween event rewarded a mount (a flying witch's broom) so anything is possible I guess - events generally already reward costumes and armour so that is guaranteed.

You're new to level 50 stuff it looks like, if I'm assuming right based on your weapon/shield. any time you're in a group, enemies link. when you aggro one enemy that's linked, all others in that link aggro you as well. This lets you use flash/ect to grab the aggro of everything around you. Enemies in dungeons are automatically linked, enemies in the overworld are only linked when you're in a party.

I have a level 60 Paladin, this is just my legacy toon i hardly played lol.
I feel that spamming Flash isnt fun. I feel that we can use another AOE attack. Maybe Shield Bash spell that does dmg to the mobs in front of you which also increases ENM.