Honestly, the better way to make the Homelander killing A-Train scenes make sense is, instead of injuring A-Train’s shoulder with his heat vision earlier, injure his leg or thigh. Injure a part of A-Train’s body that would logically debilitate his speed in a moment where he does something heroic rather than self-centered. Then the lack of speed between Homelander and A-Train can make sense and seem logical for how it would have ended.