I believe that Rotational spawns is good, what i would suggest is a ''fixed rotation'' so we will have per month at least once every set. Some sets are more useful to ones than others, but i think all sets have good pokes to hunt. So since we have 9 total sets, i would suggest each set to stay for 3 days, therefore in 27 days all sets have been used, i would say the last 4days would be from votes like we have now.
My suggestion would bereduce the amount of sets, Supprot set is kinda irrelevant i would say, and especific Weather teams, just lacks enough mons to be relevant enough imo. In any case i will leave a suggested set. This is just an opinion dont critize me too much ok x)
SInce we have 4 possible spawn areas, and 4 possible weather, lets split them shall we.
About the current spanws in ea sets im give some suggestions, and trying not to be too broken:
Offense
GUILD ISLAND: Dratini Marill
GUILD ISLAND FOREST: Snivy Larvesta Abra
GUILD ISLAND CAVE: Beldum Larvitar Gible Sneasel
GUILD ISLAND FALLS: Jangmo-o Froakie
Balance
GUILD ISLAND: Frillish Mantyke
GUILD ISLAND FOREST: Ferroseed Tangela
GUILD ISLAND CAVE: Rotom Deino Porygon
GUILD ISLAND FALLS: Pawniard Scyther Meditite
Weather
GUILD ISLAND: Mudkip Omanyte Kabuto Lotad Qwilfish Wingull Horsea
GUILD ISLAND FOREST: Charmender Bulbasaur Torkoal Seedot
GUILD ISLAND CAVE: Drilbur Gligar Hippopotas Buneary
GUILD ISLAND FALLS: Alolan Vulpix Snover Snorunt Spheal
Trick Room
GUILD ISLAND: Corpish Marill
GUILD ISLAND FOREST: Solosis Bronzor Slowpoke
GUILD ISLAND CAVE: Mawile Alolan Marowak
GUILD ISLAND FALLS: Audino Espurr Whismur
Stall
GUILD ISLAND: Alomomola Slowpoke Mantyke
GUILD ISLAND FOREST: Foongus Chansey Clefairy
GUILD ISLAND CAVE: Skarmory Sableye
GUILD ISLAND FALLS: Alolan Grimer
I cant come up with low tiers spawns XD Not that easy to make the spawns balance based on the ''set type''
I just gave an idea, on how to maximize spawns. trying to have 5 sets which makes 6 days ea, 3 days rotation. therefore ppl can hunt one set twice a month. The sets are pretty straight forward, where high tier mons appear in a specific set.
In short, what i suggest, is a rotation spawns, fixed, 3 days each and 5 sets. With this we will have each set twice a month.