I feel like rain teams have been optimized to a certain archetype and there's not much room left for innovations until the arrival of Crawdaunt or maybe Scald tutor. Pelipper - an electric type - two water abusers - two mons that will do whatever you want.
What I feel is maybe the best core, from my experience and from other people teams has to be Basculegion, Zapdos and Greninja.

sinergizes with Greninja because it is physical, Wave crash recoil is hardly a problem since its main purpose is to take hp off enemy water resist and force random tera water, also Aqua jet allows you to at least try to outplay Kingambit, something its female counterpart could only do by running substitute.

is the best thing we have left from last generation and usually the electric type you want on your rain, as you always want one to beat water types and abuse things like tera water garganacl or galarian slowking while keeping momentum with volt switch.

with battle bond is hands down the most powerful late game mon you want to click a water move on. After the Basculegion suicide, it becomes easy to get a kill and proc its ability, then you just kill everything. And of course, it helps vs Kingambit with its typing and priority move.
There are for sure interesting alternatives such as using Thundurus-T or Volt absorb Pawmot as your electric type to help your Zapdos matchup, and good abusers like the almighty Golduck that can run any kind of black magic with access to NP/Encore/Disable/Hypnosis, good offensive coverage and Swift swim. But let us get back to our aforementioned core.
Adding brother Pelipper, we have only two spaces left for pokemons, and there are a few problems we have to deal with :

absolutely destroy us if they can set up, especially under screens.

will leave us no winning options if deployed while rain is down.

are special attackers we can't allow to gain momentum.

win condition is still a threat.
And lastly, we have no hazards control whatsoever. Many holes to fill for only two pokemons still allowed. This is where the fun begins and everyone has its own take. I've seen people run Iron treads and Eject pack Amoonguss with bulky tera fairy Zapdos. I've seen people run Ting lu and Kingambit, some going Ting lu/Great tusk in an attempt to keep up with the hazards game. Some just ignore hazards and field one special and one physical tanks, a move that basicaly put your team on a timer even lower than what you would already expect from the offensive rain playstyle.
I am one of those as my two mons are as follow:

specially defensive with Eject button and Spore for momentum.

tera fairy is what I use as a check to the physical threats. It has the luxury of not being as weak to Zapdos as the others.
I felt like I basicaly did a RMT in the wrong forum part. Now, tell me about you. Which mons do you choose to run as your two fillers ? Are there any good unexplored options, what do you think of the 3 mons core I spoke of ? Do you feel as well that Zapdos is a real threat or am i just completely paranoid ? What do you think of rain teams in this generation ?
Anyway, I am going to try out Hydration Rest Whirlpool Alomomola, maybe it is the best way I can ride the wave to victory.