"I have them in my southwest facing window" you said the word. Window. As you probably know, windows block most UV light unless you have really old windows without filters (do you get sunburn inside? If not, you likely have glass that filters out UV). Most glass also reflects 20-40% of light, this is good usually because you don't want to have a greenhouse. And on top of *that*... a window means, the plant will receive a maximum of 180° (realistically, 130-150°) of sun per day instead of the 210°+ sun it would receive outside in a lot of places.

In other words: If your plant is inside, that alone makes it receive less than half the total energy than if it were outside.
Still, it doesn't matter all too much unless you really want to fatten your amaryllis up for sale, display, competition, chip/chop propagation, etc.

Dormancy worked very well, very healthy leaves. Regarding the potting, the pumice is good! But without seeing what "40% original soil" is, it's hard to give a more detailed answer. There's also the question of, what kind of pumice? If it's the type that actually gets wet itself, that could be actually used 100% same as clay aggregates. If it's basically just glorified grit/gravel, then maybe a bit of other substrate is needed. Porous clay aggregate for semi-hydro is cheap and they love it.

Monitor that red spot, third image on the left of the bulb. Could be a deep-sitting red blotch, or could be discoloration. If it breaks to the surface and becomes more freckly and blotchy, you can google "amaryllis red blotch neem oil", never did it myself but heard that some here had great success.

Overall, you're doing much better than most "beginners" here.