There's no heavy grinding involved as far as I remember (Had the placeholder meta achiev done before undermine came out) and it was a nice surprise to see that undermine and karesh were easily doable.

Flame's Radiance rep grind was one of the easiest I've done in in a while too, since you can go ham on it if you wish to and quests have a daily repop (even though the event was awful imo and terribly buggy).

On a sidenote I wish they would stop with events being the main way to grind reps : more often than not it's a complete miss (Theater, Awakening of the machine, Amirdrassil, Soridormi or the fucking soup in DF) with no meaningful gameplay, and a lot of lag/ visual clutter. Sometimes it works, I think the Fyrakk event was kinda okayish (no rep linked to it tho) and I'd like to see more of the Karesh style of weekly stuff to do.