With Onomat back in the competitive scene. The meta undergoes another transformation. It is not clear how exactly the meta will be but, key points to keep in mind:
Onomats have a pretty nice match up against Harpies (potentially starting a slight decline in representation)
Handtrap decks like Fire King and Yosenju will have bigger representation to counter Onomat
If a decline in the number of Harpies happens, Thunder Dragons struggle even more in this meta. Not to mention, they lose to Onomat and so might even lose its spot in future Tier Lists
Blue-Eyes has a slightly unfavorable match up against Onomat but the rise of hand trap decks probably will compensate.
Onomat entering the meta is very interesting for Harpies. On the one hand there is the Loading... version of Onomat version which Harpies struggels against a lot. Loading... can only use its effect to bounce if a Spell/Trap card or effect is being used, and if Trunade bounces all the backrow that leaves Harpies pretty defenseless. Since Onomat has a lot of Level 4's, they can easily end on Loading... and another monster through which Harpies can only play if they draw Loading... and can only OTK if Harpies draws a 4-card combo with no additional interruption from the side of Onomat. Thankfully for Harpies, the Trunade version is not that common at least in Game 1. People seem to prefer }Gagaga Sister} which gives Harpies other problems since Sister allows access to the Rank 6 toolbox and searches for a way to extend or force interruptions. Harpies can just go first agaisnt this variant and prevent the Onomat OTK, especially with a well-timed Book.
As such, Harpies will need to adapt in the Side Deck and put in some cards to counter Onomat if they want to stay as the undisputed best deck of the format
Harpies have a new rival in Onomat which makes the matchup reliant on the coinflip (in favour of who goes 2nd) and seeing Loading... on Harpies' side to deal with Loading... / Loading... and Loading... / Loading... on Onomat's side to deal with backrow.
Onomat has the advantage of having consistent access to floodgate monsters like Loading... and/or Loading... on their first turn while Harpies have the draw power of Loading... to see techs but they don't really have monsters to setup on their first turn to control onomat's plays. Not to mention, Onomat can easily see Loading... / Loading... with Loading... without risk. Basically, Harpies have to draw Loading... in their opening hand to play going second and to cross their fingers going first while Onomat can have a decent set-up turn one and can easily OTK turns 2/3.
Harpies can use almost any tech in the game, so they will probably find a solution to deal with Onomat, but they will still need to draw it.
Harpies remain the number-one enemy in the format. However, Onomat being re-introduced into the format adds another potential thorn in Harpies' side. As a deck that can run Loading... (albeit not the common variant at the moment as most are sticking with Loading... to have a more well-rounded matchup spread), make Loading... with ease, and pressure Harpies with OTK threat, Onomat generally has a positive matchup against our winged friends. However, there are relatively easy adaptations Harpies can make (especially games two and three) to overcome the Onomat Matchup. Cards like Loading... , Loading... and Loading... (for the Loading... variants) are among the several cards Harpies can add to their Side deck to dodge the OTK threat of Onomat, and OTK themselves on the crackback.
The introduction of Onomat back in the format is welcoming for Fire King. With it, Fire King gets a new matchup which is favoured at least in Game 1. With their ability to summon Loading... Turn 1, prevent OTKs with multiple handtraps, and have monsters which can float/blow up the board, it is pretty easy to see why the matchup is favoured at first glance. Of course, Onomat has some counterplay. They can just draw their Loading... to put Arvata face-down or open up extenders to not lose to 1 negate. Loading... can play around Loading... by simply attacking for 4000 directly, forcing the Fire King opponent to draw Loading... or Loading... . It can be hard, especially post-side as they could side either Loading... to deal with Loading... float or Loading... to OTK without worrying about handtraps. With Onomat rising, Blue-Eyes has an even harder time in the meta which is good news for Fire King since they struggle against Loading... .