Interestingly, a high G maneuver may have lower AOA than a stall maneuver. The MiG 21 spike inlet is 1950s vintage, also seen on the SR-71, used to solve the problem of slowing supersonic inlet air to subsonic flow that was then fed into the turbojet.
The MiG 21 was designed more for hit and run and is not as versatile as the F-15 Eagle, which suceeded it and it's F-104 Starfighter and F-4 Phantom contemporaries in the 1970s.
It is doubtful a spike inlet would be anywhere near as effective as the F-15s inlets during low speed, high AOA maneuvers, but neither would the rest of the plane. It would be far better off to stay with its strengths.
The MiG 29 and Sukhoi Su 27, developed and put into sevice just after the F-15, feature similar air intakes, as does the fastest of them, the MiG 25.
In seems that the designers reasoned that the nose of the plane itself could be the "spike", placing the turbojet intakes on the side (further back) inside the shock wave "cone".
For subsonic high AOA maneuvering, the advantages of placing angled intakes on the side (or underneath) are obvious, and could lead too ... a better pitot tube design for GA aircraft.