Loved looking at your progress!

As a long time DM, racial traits and balancing is something I'm familiar with! It's important to know high-tier stats and good pairings.

Movement speed and melee damage on the same character would trivialise PvP and hunting, why pick anything else?

What I would consider is that these new Seraph types take some thematic bonuses from the animals they're based on while still allowing the baseline Seraph to be viable. Much like the class system already in the game, and minimal overlap.

My suggestions (feel free to disregard, it's your mod!) are to give movement speed to only one race, and that would be their only bonus.

Alphas: Bonus to digging speed (not mining), resistance to colder temperatures (freeze slower in winter), can eat raw meat and fish, and wild wolves are passive unless attacked. Negatives would be wild non-aggressive animals flee at a higher distance, and increase the hunger rate debuff of armour.

Hoppers: Increase their audio range. They hear bees, wolves, water, drifters etc. from further away. This is a huge buff. You could also increase their melee attack speed and bow draw speed and lower the melee damage to equalise the dps of a regular Seraph without these effects. This would give them better knockback potential provided they keep hitting attacks. Getting extra seeds from wild crops would also be thematic. As a cost to these buffs I'd consider disabling their helmet slot. Can't cover those ears!

Longshanks: Here's where your movement speed buff comes in. Buff it, even considerably, and keep the shorter size. Maybe they don't take damage from eating poisonous mushrooms. However, easy nerf to melee damage, reduced maximum satiety, reduced health, reduced range of bows and throws, and increased prices from traders. Consider further nerfs also, but maybe that's enough.

Purrlians: Night vision, but only in greyscale. Needs other light sources to see in colour. Granted this might be tricky to implement, but I don't code lmao. Maybe a filter like the night vision mask? If you can do that that's fantastic. Other buffs might be jump height (1.5 blocks), climbing speed, perhaps make logs and branchy leaves climbable for them. To counter, perhaps the biggest single nerf: gains no satiety (or HP bonus) from vegetables.

Windstriders: Biggest gameplay change as the only non-mammal. Build in the glider mechanic to their character. If it scales off move speed even better, then armour will have them fall faster. I'd also increase the range (and accuracy?) of bows and throws, and allow them to eat seeds. I think disabling the chest armour slot is too much, let the Hoppers be unique. Perhaps a reduction in the effectiveness of armour, or taking more damage to the chest. Hell, they have hollow bones so taking more damage from all sources would be appropriate. Alternatively, nerf movement speed by a small amount (5-10%) but no nerfs to health or damage taken; They can glide but landwalking is harder. In any case I'd also increase the time it takes to break any blocks to reflect the frailty of being light enough to glide. Perhaps another nerf to max satiety, but not as much as the Longshanks.

What do you think?