if you have free power then you should mine but my advice dont mine bitcoin. try other mineable coins. they are easy to mine and very much profitable than mining bitcoin.
You are correct , mining Bitcoin is pretty much useless on a PC , you need ASIC for that.
https://whattomine.com is the best place to check based on GPU, CPU, ASIC
You can also check
https://electroneum.com, which tries to bring mining to smartphones