ProfessorMonks 5G means 5G or below, which allows using all the supported protocols. It provides maximum compatibility and overall connectivity/performance. It's the default mode in AOSP and why it says it's recommended so people know which one to go back to if they have issues. We do not plan to change that.
Using our added settings ("4G only", "4G or 5G only" or "5G only") requires having VoLTE/VoNR for working calls, will lose connectivity if only 3G is available, etc. It is not the default for a reason, and we aren't giving a general recommendation that most people use the attack surface reduction feature. It is there for people who can accept the downsides for reduced attack surface. It may improve battery life but it can also reduce it, that depends a lot on the available connectivity.
AOSP recommends the default setting good reason. Many people already have issues with setting "4G only" and not understanding that lack of their carrier fully supporting it is why they don't have working calls anymore, etc. We don't want to make changes which would make this worse. The settings are for people who understand the consequences.