Hey Myen'Tal. Yeah the reason for the prevalence for Marines and the sheer number of releases, is they essentially rebooted the entire Space Marine line. In my opinion they've modernized and simplified the range and in the future the Chapter Tactics should stack cleanly on-top of the very clean dataslates.
In the weeks since the Marine FAQ there has been great variety in top tables at tournaments at the very least. You had a double Drukhari duel at a finals here in the south of the USA, Sisters winning a major event over in the UK, Aeldari winning here and there. Genestealer Cult and even Blood Angels. All "off meta" armies.
The balance has been restored to a large degree, but its still an uphill battle against Marines, nothing like it was. For the most part there has been really good balance in the game throughout the edition. There were 3 bumps in the road IMO. The Castellan Knight, the Alaitoc Flyer list, and then Space Marine meta. Which was basically all within 6 months of each other.
With all of that being relativley patched, its really not the scary anymore. There are tons of good options for every army. And all of the armies have a niche. The mainstay factions are really strong: Space Marines, Asuryani, Chaos are sort of the top dogs. With Orks, Drukhari, Sisters and Tyranids, Genestealer Cult and Guard being Tier 2 that can very much win any event in the hands of the right player. Ad-Mech, Harlequins are a bit behind them but Necrons actually have great numbers against Marines, but they struggle against some of the other factions.
Some of these armies aren't meant to go 5-0 at an event, such as Harlequins. But you can crush on the regular with any of these armies just playing regularly with friends.
As for AoS I cant speak to it specifically, but it has the same issues from what I've heard. With Slaanesh and Daughters of Khaine dominating for a good long while.
Its important to remember GW games are big ships and take awhile to correct course. But unlike the past there have been LOOOOONG periods of total stability with only a few outliers. As opposed to editions previous where the long periods of consistency were usually consistent misery. The internet sort of amplifies the negatives, but when you are just out there playing games, its really been a great edition with very little worry about outside a few tough months.