Firstly, forget your obsession with saying "monster power" as an alternative to energy and powers, especially when it comes to Michael's powers and his Apostle. The Power trait isn't about powers, it's about energy - "power" in terms of energy and energy fields.
Did I not say multiple times that his power affects energy? Which would include monster power? Which would affect powers? I'm pretty sure I said this over five times already.
Michael's power is basically the manipulation of energy fields/electromagnetic fields relating to the high end of the EM Spectrum, particularly around nuclear energy aka ionising radiation (we'll get to that), and is why he can mask his own energies better than other superhumans and why his physical durability generally is better than others of equal level.
No indication of anything after ionizing radiation. In fact, it was explained superhumans are generally more talented at hiding their monster power the more stoic/emotionally disconnected they are (and the opposite is true for sensing), and Michael is the definition of disconnected from other people. As for his "increased durability", that would mostly come down to absorbing the edge off of energy attacks when they hit him.
He can absord energy-based attacks at level 1 and emit a literal "shotgun-like" radiation burst called (wait for it) Ionised Red... He literally fires a blast of nuclear energy with high intensity ionising radiation that results in whomever gets hit with it, being ripped apart at the cellular level.
Level 2, he gets an objectively better version of Ionised Red in the form of Radiation Beam - Higher output and in focused beam rather than a "conical blast".
Radiation knife is basically just him stabbing/slashing an opponent with concentrated ionising radiation. Funnily enough, Michael can potentially generate a "Radsaber" (radiation lightsaber) instead, but that one might be a little too on the nose.
His radiation attacks damage superhumans, slowing their abilities to heal (cellular/genetic damage), and even give them literal radiation poisoning (cellular/genetic damage)... That's all to do with ionising radiation.
Cool? So he can produce ionizing radiation. Why does that matter to the current subject?
So, for the third time now, you have agreed with me that the MC can be damaged and possibly killed by high exposure to radiation/radioactive particles.
Where? WHERE???? WHERE DO I AGREE???? The ONLY thing I said is that MONSTER POWER, as in the energy superhumans use, resists MC's and Ella's shapeshifting. Michael's MONSTER POWER, meanwhile, is also specifically monster power of the trait that can mess with energy, INCLUDING MONSTER POWER, so his effects would FURTHER interrupt MC's shapeshifting BEYOND what other superhumans, like Cole, could do with effects that persist inside MC's body.
You can't ignore the existence of monster power as a major player in this discussion. Everything any superhuman does with their power is constructed, fueled, and imbued with monster power, which has been shown and stated an innumerable amounts of times to interfere with the effects of other monster power. Yes, MC COULD be damaged and possibly killed by high exposure to radiation.... If it's made and fueled by monster power. Other radiation, we have no reference on.
To interject on this, as it relates to what I've written above, it's "space" as in space and spacetime, which is where gravity and (theoretical) dark energy come into play, and their effects on spacetime.
Yes, but you'd think a trait named space would work from space back onto gravity and dark energy, rather than backwards. The trait of Ether seems to be closer to the philosophical element of ether/aether mixed with some current understanding of space, hence the name Ether in the first place, though I'm not saying that with certainty, since there's clearly a lot we're still gonna learn about Alice's powers.
The takeaway from all of this should be that you can't try and science pseudo science while conveniently ignoring the pseudo.