Preventing BFA in WordPress without using a plugin

One plugin-free layer of protection you could implement is to route your traffic through a site like CloudFlare that has built in brute force protection. The free version is a great layer of protection with paid tiers if you need the added features. I have used this for several of my sites.

I am with you in that I try to use as few plugins as necessary.

*note: felt this would have been better as a comment but did not have the necessary reputation.*