Let' talk about the balance of the three factions in the meta. I want to ponder three questions: How did we get here? How bad is it? and Will it get better?
First let's dispel the notion that the players in the top 16 at worlds selected their lists based off of what was thematic or new. Those top 16 lists were selected because they gave those players the best chance to go far in the tournament. They were selected for the ability to consistently score more points than the other player's list. No one was going to be taken off guard by a merc hunter list, so taking your opponent by surprise did not factor into those selections (except maybe for Shyla).
How did we get here?
The last meta was dominated by spies and troopers. Most of the top lists included Blaise, Stormtroopers, Heavies, Cross Training, Leia, Sabs, etc. Mercs were on the fringe with the Bantha and "Scum good stuff" (HK's/Bossk/Tuskens/Nexus). Mercs had very little access to the amazing spy and trooper cards. I think most would agree the ranking was 1. Imperials 2. Rebels 3. Mercenaries.
Then Jabba's realm hit, giving a third trait, "Hunter", to equal or surpass Troopers and Spies. Mercs got Shyla, Onar, Vinto, Weequays, and Jabba to go along with Greedo, Bossk, HK's, Ig-88, Boba Fett, and Trandoshans all with the Hunter trait. Rebels have alliance rangers and Biv. Imperials have the inquisitor. At this exact point, right after Jabba's hit, and right before the rule changes happened, I think the three factions were pretty balanced. I was personally running Rebels with Luke/eRangers to great effect, winning myself a regional tournament. Imperials were still around and still insanely popular, with elite Jets supplanting Heavy Stormtroopers, and Terro adding a new dimension to Imperial lists. People were still experimenting with Mercenaries, and I don't think I saw any Merc lists in the top 8 at that regional. (There was an imperial Rancor list though)
The "points per figure" rule nerfed 3 figure groups (e.g. elite Stormies and alliance Rangers), and especially nerfed any groups that used "reinforcements". The rule was absolutely necessary, because running a figure away to preserve the whole group's VP's led to some very frustrating strategies. Rebels and Imperials both took significant hits, while Mercenaries remained completely unscathed.
At first the points per figure rule change seemed like it would help Rebels, with their abundance of unique single units, however most of the single units in rebels are either overcosted (Han, Chewie, Diala, Fenn), too fragile (Leia), not mobile enough (Obi), or don't hit hard enough (Davith, Lando). Rebels didn't get nerfed as hard as Imperials, but they were already behind the curve, and the nerf was a setback to their new vanguard units, the elite Rangers.
Now Mercenaries are unarguably the best faction, but..
How bad is it?
15 of the top 16 lists at worlds were Mercenaries. Of those 15, I think all but mine had 2 sets of elite Weequay Pirates (and that's mostly because I was not going to drop another 75 bucks for another copy of JR). Hidden elite Weequays hit just as hard as HK assassin droids. They also have 1 more health and cost 1 less. HK's were the best unit in the Mercenary faction before Jabba's realm dropped, and Weequays beat them in every category. The fact that they can hide themselves dominates close range shooters like elite Sabs and elite Heavy stormtroopers. If there is a unit in the game that could use a slight nerf, I'd say it was the Weequays. (maybe make it so they gain a surge power token instead of hidden, since power tokens are gonna be a thing).
Other than pirates, I don't think Mercenaries are that out of balance. Imperials still have access to spies, and elite Jet troopers are among the strongest units in the game. Stormtroopers and Heavies took a pretty big hit in this meta, but Terro and Dewbacks are very viable. Rebels got Jedi Luke, who can win a game with a well timed Son of Skywalker (which actually sucks if you're a high skill player). Elite Rangers are good, but not overpowered.
I think there are 2 big problems with the meta and neither of them is that Mercs are too strong:
1. Son of Skywalker and On the Lam are too powerful. Where these cards are sitting in your command deck will win or lose you games.
2. Sniper units are significantly better than melee units. Units that can shoot you from across the map should not hit as hard as units that need to get up close.
Both of these problems lead to the "boring" type of play you saw at the highest levels: hiding behind your doors until you have the command cards you need to have a big turn. Both of these problems are much bigger than the very close balance of the factions.
Will it get better?
In a game like this where new figures are being released every 6 months and rules changes coming just as frequently, no faction is going to stay in power for long. However, the droid wave seems to favor the Mercenary faction more than Rebels or Imperials, so if you're getting tired of Mercs, you'll probably have to wait for "Heart of the Empire". I expect HK's to make a slight resurgence and I expect IG-88 to be a viable list centerpiece. I think 0-0-0 adds very little to Imperials for skirmish, but BT-1 should be pretty good. Whether that's enough to push Imperials back into the top of the meta is doubtful. Hera and Chopper seem balanced, but not enough to put Rebels on the same level as Mercs.
I haven't taken a deep look at Heart of the Empire yet, but it seems like there are a lot of big changes coming that will really shake up the meta. I'm really hoping that the brawler buffs will be significant, because sniper units are getting a bit out of hand. I'm sure by this time next year we will have completely forgotten about the 6 months or so that Mercs sat on top of the meta.