Yeah; the skin is a bit drier, but as you say, that’s generally not an issue for armpits.

Soap binds to oil and water, so it’s great for stripping oil any anything on/in the oil from your skin. But there’s lots of bacteria and fungi on your skin/in your pores that soap won’t get rid of. A lot of them are beneficial, so we don’t want to disturb them, but armpits generally get over-colonized by smelly varieties.