Why you need to go to 5.1.4 instead of 5.2? Who told you that?

1. I meant to say that not all of my extensions are compatible with 5.2
2. It would be nice to have the option or flexibility in Joomla to decide which version to upgrade to. (I could do this manually by uploading the 5.1.4 update but that circumvents the extension/plugin version check in Joomla)

That would be a bad idea. We always want people to be using the latest release.

1. sites are running J4.4.9 or 5.1
2. we do incremental updates/upgrades to minimize issues such as extension and plug in conflicts
3. I’m not typically an early adopter of Joomla updates (ie from 4 to 5) because of bugs

We eventually update but these are the reasons we prefer to do it in a managed and controlled way to minimize disruptions to our clients

That would technically mean that we have to keep entries in our update sites for all versions. I don't think that's a good idea.

This should be closed. It is bad practice not to install the current version espec if there is a security issue. As already stated by the op they can still chose to update to an out of date release using the upload and update option. Joomla shouldnt be doing anything more ergo there is nothing more to do here.

5.1.x is not a supported version anymore and it's not recommended to use it. Please use only the latest version of the supported versions.

Before new (major/minor) versions are released there is plenty of time to test before.