By the West differentiating between the supply of anti aircraft and anti tank missiles, as opposed to supplying MIGs, is literally a case of semantics.
Take two examples.
A Russian tank points its turret at a block of flats. If nothing is done, the block of flats will be destroyed and many will be killed; not everyone can leave. If anti tank missiles are fired at the tank, it will be destroyed and the people in the flats will be saved. There is no difference between an anti tank missile being fired from a launcher on someone’s shoulder as opposed to a missile being fired from a plane. BOTH WEAPONS SYSTEMS ARE DEFENSIVE
A similar tank points its weapons towards a long line of refugees. If nothing is done, the refugees would die. If an anti tank missile is used, the refugees will be saved. Similarly, if a Russian plane fires a rocket at the refugees, they will die but if a Ukrainian MIG takes down the Russian plane, the refugees would be saved. Again, both systems are defensive in nature.
There is a very grey area between defensive and offensive weapons. The best way of making a differentiation is if the Ukrainian MIGs then went into Russian territory; then the planes would be seen to be offensive.
Whatever weapon system is used, their primary objective is to save lives by destroying the OFFENSIVE Russian systems.
The MIGS are defensive as they are DEFENDING the sovereignty of Ukraine
Send the MIGs to Ukraine, with them being piloted by Ukrainians