I do instructor led X-Bike sessions at my local gym ( They’re called “Trixster”) – Not spinning as such, but a similar idea which I suspect attempts to more closely resemble actual cycling. ( Including variable spring tensioned handlebars & pedals whch allow free-wheeling as opposed to directly attached to the wheel mass).
By the end of these 45 minute sessions, you are invariably drenched in sweat and you also have a small pool of the stuff on either side of the bike.
They are hard workout sessions, but I’m not so sure they give me any noticable greater abilities on my bike.
( Still, I really do enjoy them, so not too bothered).
Chris