Multi-tenant organization - confusing documentation

Hey there, set up MTO, I've been told this has a 'unified' Teams experience but I think that is a lie.

UserA in TenantA is synced to TenantB
UserB in TenantB is synced to TenantA

If UserA searches for UserB, they can find the person, start a chat, but this 1:1 chat lives in TenantA.

If UserB searches for UserA inside of TenantB and starts chatting, the first chat that existed doesn't sync or update. It's a separate chat in the opposite tenant.

We need to split into 2 tenants for regulatory reasons and we were hoping to have a more universal 1:1 chat experience, but is this going to be the reality?

This doesn't really 'feel' like multi-tenant, it just feels like 2 people that happen to exist in 2 different teams orgs.