carbon on road shoes isn’t really for weight saving, its for ‘power transfer’ and comfort.
And its massively noticable. Used to have some expensive Lake MTB shoes (about 160 retail) and they were very stiff for walking in, and felt stiff on the bike, but using them for road, after about 40/50miles my feet would be curling up and aching.
Swapped to some much cheaper ‘Exustar’ (formally Exus) carbon shoes (SR220/221?) from ebay for about £30, someone had bought them, not fitted so sold for a lot less than new. but generally about £70-80 for anew pair. And their great! Daft as hell for walking in, but very well ventilated, dry quickly, most perfect fitting bike shoe I have ever worn (most shoes are normally always too narrow for me, making top of foot ache after a while) and they take very kind of road/mtb cleat going (which Lake/Spesh/Sidi shoe’s often do not have, you have to choose at time of purchase).
Anyway, for MTB, no, the carbon sole gets wrecked from walking on gravel/rocks within a few minutes, not damaged, but look scruffy on the underside now, for even amateur road and touring, yes!