Gnomish infravision

So, this is a terrible case of thread necromancy - my apologies - but something which seems to be ignored in these calculations (re: Elf) is the ability to cast arcane spells while wearing armor (I believe gnomes have this as well) and yet it is not factored into the racial cost. This is a huge advantage over humans but always seems to be almost, handwaved off as “just a thing.”

I’m wondering how to reconcile that as I’m working on adapting a few races into my new campaign and this was the best discussion I found on the topic.

Thanks!