I don't think you'll find a really satisfactory answer to that question anywhere, the two platforms are very different, and both are relatively secure.
Like you say, Windows is a more appealing target due to numbers alone... so a better return on investment for people looking to spread malware.
Apple does have one benefit though -- by default, macOS is configured to only accept software installs that are from apple-signed developers, which provides an additional layer of trust when installing new software. So, if you attempt to install some application on your mac from a developer that isn't approved/signed by apple, you get a worrying message about it. The software isn't necessarily bad, but the message that you're given is strongly worded to make you think twice about whether you trust that developer.
On the other hand, when you install Windows software, you get the same generic UAC dialog box no matter who provides the software. People are trained to click YES without giving it much of a thought because it comes up every single time you install a program on Windows.
So, that's one way that the average user is slightly more protected from themselves when using a Mac. It's not bullet-proof, though. Bad things can happen to good software.
Example: I use a well-known video transcoding application called Handbrake on both Windows and Mac. It's legit software, and well-respected for the quality of the audio/video it produces when converting between formats. Somewhere along the line, the latest version was replaced (on Handbrake's download site) with a copy that included malicious code. Anyone who downloaded and installed it on their mac are infected with some nasty malware.
Thankfully, I didn't download a new version recently, so I'm unaffected. However, I just read an article today that the developer (Panic Inc.) for another piece of software, Transmission (in my opinion, the best FTP Client available for macOS) did get infected by that malware-laced Handbrake download, and as a result a good portion of the soruce code for Transmission has been stolen. Is there a chance that vulnerabilities will be uncovered in Transmission when the source code is examined? Idunno. I'm considering using a free open-source alternative on my Mac for a while, though.
If that wasn't a long enough post, here's some additional details about the two recent hacks in case you find these things interesting (ha)
https://blog.malwarebytes.com/threat-analysis/mac-threat-analysis/2017/05/handbrake-hacked-to-drop-new-variant-of-proton-malware/
https://panic.com/blog/stolen-source-code/