Please don't shut up, that was really helpful. Thank you so much!

Still looking for a few more opinions :)

I think you should stay in tier 2 for now, but I see a future tier 1 artist!! Personally I don't use Ibis, but I shall see what I can come up with ;)

Your lighting looks good to me. I would work on grounding a little more. In one of the examples (the third I think?) the manes and tails looked like they were hovering over the grass lol. One thing that really sticks out is your hair painting. Really watch your flow and the way the strands are going. While flyaways are important, I think you may be going a bit too far with them. A lot of the strands criss cross, and this adds a less neat effect. (if this makes sense) When I paint my flyaways, especially the larger ones, I add a slight shadow beneath it so it doesn't just cross with the other hairs, it looks like it's overlapping, or "flowing in the wind". XD I would also try using a less pixely brush to add a smoother effect. Add a slight shadow underneath the hair so it looks a little more realistic :)

As for the muscles, like Mish said, study some photos of RL horses, and I would also recommend studying an equine muscular or skeletal chart. Here are some tutorials that are quite similar to my own techniques, I think you may find them useful :)

Hope I could provide some half decent tips xD

Thanks :)

Do you think this piece is tier one worthy?

Yes,
But your pieces have to be consistent with the quality to move up ^^.
In my opinion though

That's what I'm aiming for ;)

Yes it is Gem! Amazing work :)

Thank you!

My most recent piece. Tier one?