This feels like something of a perennial issue with Legends of Runeterra, seeming to emerge despite any/all balance patches through the beta, but there seems to be a real balance problem across the regions. (Note that I'm taking the https://lor.mobalytics.gg/meta-tier-list tier list as my source of truth here.)
On the surface, the games balance seems pretty reasonable - each region shows up in at least one S or A tier deck, and there's a decent array of archetypes available to players. But three regions dominate that tier list: Shadow Isles, Ionia, and Piltover & Zaun. Together, they show up in some 87.5% of meta decks. And it's not hard to see why - SI and P&Z have access to good card draw and damage based removal, SI and Ionia have access to healing, P&Z and Ionia have access to useful aggro tools with Elusives and Direct Nexus damage. This was true throughout the beta, and remains true today despite Rising Tides.
Every other region feels like it's just playing a supporting role to these three, which are doing all of the heavy lifting for defining the metagame. The result is a lot of less exciting deck-building choices, and ultimately less interesting match-ups because you end up running the same "SI Control" package to make any control deck, etc. Many champions (e.g. Lux) end up feeling like a worse version of some other "meta champion" (in this example, Heimerdinger) because of the added burden of being outside of one of those "meta regions."