This is one of the strange things Conitec did:

that the send_var_to is bound to an entity, not
a client-ID.

This should be changed !
In a way, that clients get an ID number or another type of ID,
so that the server can communicate with exactly this client.

So even if you create no global entites (all local, communication only by variables/arrays)
you are forced to create at least one global entity.