So, what are the max stats? I've been stat breeding ryoris and once their stats reach 100 inborn they're not affected by prismatic philters anymore...So, is 100 the max stat?

Yes, 100 is the max stat. I think it's 2000 for health.

As Shayni said, 100 is max for Strength, Agility, Intelligence, and Dexterity, 2000 is max for Health. I think 120 is the max for Mana, but you can't get that unless you have higher-ranked essences, I believe.

120 is the general current mana cap, but you can only get it a) if you're doing a fabled species (Enhanced/ Mystical essence, Exclusive pets, somehow finding a wild 3-or-4-star nephini(? I have no idea if you can find anything other than 2-star pets in Astryl's Vale, actually, so I have no clue if this one is possible), some expensive ny'vene from the Arena shop), or b) manage to find 4-star common species to work with.

Currently there is only one exception to the 120 cap, and that's some Exceedingly Expensive ny'vene from the Arena shop, which have a cap of 130 (Epic (4tp) rarity venes seem to be vary a bit, but might have 120, Legendary rarity venes (6tp) seem to have the general 120, but if you manage to get a Mystical (8tp) vene, it's 130)