FWIW, my view is that this is about inventive and well-coordinated combined arms. MBTs are part of that. Bradleys and Marders are part of that, along with BMPs. Ukraine has shown it's very capable of coming up with innovative tactics. Back when this war started many assumed Ukraine didn't stand a chance. They've shown the world that their indomitable spirit, courage and above all technical competence, has what it takes.
Neither Challengers or M1's are great for Ukraine's needs, least of all the Challengers. Leopards are a far better bet. If giving Ukraine a few Challengers acts as an incentive to get Leopards on trains to Ukraine then that will be worth it. They do need the rest of the combined arms suite, though. That means a wider range of kit to cover the whole of that tactical requirement.