I just did the main missions and the gold colored side quests and never had an issue with levels.
This is where I'm at, and I'm consistently 3-4 levels ahead of the main quest, but I do also clear a lot of the points of interest, which can feel pretty grindy at times. Especially considering how similar every point of interest is. Two, maybe three story building, two to three treasure chests, three to four war supplies, one super elite enemy, and two to three normal elites. It's still fun, but it gets very repetitive and grindy. However, I just did the farm on Euobea with the four grain silos, creeping through the wheat fields with two mercs chasing me. It was actually very harrowing and fun.
What I'm genuinely curious about is the post board quests. Are those generic, procedurally generated quests? They all seem to be just very basic assassinate/fetch quests, and some are timed. I just started ignoring them completely because it felt like every time I finished one, another would replace it in the list, and I ain't about that boring ass shit. Reminds me of the annoying "spider are eating my grapes!" quests that kept happening over and over and over and over and over again in Skyrim, or the even worse base defense ones from Fallout 4.
There's also the hourglass quests out in the world that appear to have story content tied to them because the NPCs actually have conversations, but I've kind of been ignoring those too, for the same reasons as the post board quests.
Gold sidequests + story quests + points of interest + occasionally taking down mercenaries + going after all Cult of Kosmos members = pretty streamlined gameplay experience where leveling has never been an issue.
Playing on normal, by the way, with level scaling set to two levels below mine on lower level areas.
EDIT: Can anyone shed light on how the fucking battleground quests work? I'll get to a zone with available battleground quests, ignore them for a few hours, and they'll go gray. Did I just lose the ability to engage those? If so, that sucks. I'm now going to start going after them as soon as I get to a zone.