This isn’t true (also tagging
658Greninja). Rain is good, but it’s nowhere near close to common or top tier. It’s just another archetype of offense that works well.
Bulky offense with momentum and balance with enough firepower tend to be the most common right now. Obviously everything has pros and cons — if this were not the case, we would all use the best strategy without cons or avoid the worst one without pros, but I would check your BO/balance teams to make sure you’re not too weak to threats and work on thinking longer term rather than turn-for-turn. It takes a lot of time to learn to play these relative to outright offense, which is a big factor.
Of course, offense and Rains are good, too, but they’re not at all as dominant or focal as indicated above.