If I understand correctly, each new level of Orcs will be the result of some mutations on the previous tier?

No, I don't have enough imagination or materials; the idea is this for now:

There are basic, small, skinny archers; this is the first stage of development; you can conditionally consider it a goblin.

If they eat well, they grow into fat orc archers.

Then, two more stages of development without mutations - just strong orc axemen and shamans.

And finally, an orc-gigachad on the model of a leader; a funny fact - the orc and dwarf units in the fifth game are significantly larger than the units from the original, so the fat orc on a peasant and the goblin on an archer only reach the leader's waist - this metamorphosis should happen with magic.

In principle, you can make the fat orc without fangs, the axeman with ordinary fangs, the shaman with huge ones, and the last one with his entire mouth filled with teeth like an anglerfish.