My current opinion:
Plugins due to their nature are held to a slightly higher standard than other types of applications. Consequently, until this plugin is either fixed by the author, or a fork of it happens by someone else willing to take over then CA will not include Preclear on v6.4.1+ (It is still available in CA for unRaid <=6.4.0)
I do not know how benign the effect of installing the incorrect version of tmux is, and no matter how you term it, this patched .plg file is a hack on a non-functioning and incompatible plugin.
Previously, the same thing happened to the Server Layout plugin (it was incompatible, and @Squidposted a patch to let it work, but it was never let it back into CA until the author fixed the problem). Currently the same thing is also happening with the OpenVM tools plugin.
Alternatives do exist: Namely not bothering with preclear at all (I'm of the opinion that its not necessary, and is a legacy thing), or utilizing the scripts here.
Perhaps the situation with CA and the patched .plg will change in the future, but for the time being, it is going to remain outside of the CA installation channels until its either fixed or someone can convince me / order me to change my mind.