Which security software matters greatly. If its poorly optimized, and doesn't use Apple's framework it's going to perform terribly (SentinelOne is notorious for this) , and by default with smb on mac it will scan every single file modification over the network. If you're working with huge files over smb you have to disable packet signing, make sure the mac isn't writing and looking for .DS_Store, and make sure directory caching is turned on (its off by default).

Your experience is valid, I don't doubt that, but you can't just toss a mac into a windows optimized environment and expect it to work, you have to take that extra bit of time to do things differently.

Either way, sounds like you made the right choice then for your own org, but for the vast majority of companies introducing macs generally aren't a loss and tend to have a higher ROI.