> Does anybody know how the CPU/power impact of Microsoft's and Google's offerings are on the Mac?

It doesn't matter, because from your stated issues with Dropbox, neither OneDrive nor whatever-google-is-calling-it-this-week will provide a suitable replacement for you. They both suffer from the same (and worse) shortcomings as Dropbox.

Neither competitor qualifies as "a folder that syncs" and they both install all kinds of junk to your system.