seems to me that anyone who leaves Qatar before their legal contract is finished (and they have tied up all the ends with their Sponsor) is unable to return to Qatar within 2 years of leaving.

Wasn't that always the case? I don't know too much about immigration and sponsorship laws here in Qatar or anywhere, but I think I thought that if one breaks a contract and skips the country ......

I doubt that anyone wishing to enter Qatar legally would be refused entry. ???