OK, but I dont see Thanos able to penetrate Magneto Magnetic Force Field the same Defense that can withstand a direct hit from Galactus, Phoenix and a planet explosion. What Mags lacks to finish the Titan this one also does not have the level by itself to oppose a bigger threat to Mags defenses than that of the cosmic beings.
Will be talking of a different history if Mags accept the collective-xorn power. Or when writers could unleash the full potential of Magneto universal force enbodiment.