I would think an owner should give the GM a budget and for the most part the GM should spend that money to make the decisions on who to sign. If I was an owner I would want all major signings to go before me first and I would want justification for it before signing off on it.
The GM should hire and fire the manager but have to justify before the owner first, just as Bobby Bethard had to go before Jack Kent Cooke before signing Joe Gibbs. Both Gibbs and Bethard went before Cooke and he asked questions before signing off on it.
Supposedly the Chris Davis signing in Baltimore was an Angelos decision.
That is how it should be.
Filling out the Spring Training roster with some bodies? Your call, GM. Multi-year, multi-million dollar contracts? That need to go before the ownership.
Most large corporations and associations have CEOs, who run day to do day but have to get large decisions signed off on by ownership or a Board of Directors.