I haven't been paying as much attention this suspect test as I did for the Calyrex-Shadow quickban suspect when it dropped alongside Pokémon Home, but I mention Calyrex-Shadow now as a reminder of its Gen 8 Ubers iteration, which because of a lack of Tera and because Yveltal existed made that version of Calyrex-Shadow far more manageable. Gen 9 Ubers Miraidon feels like a very similar situation to me, where some people justifiably wanted it banned because of the warping effect it had on the metagame at large. Here's the thing about suspect tests, though- the order in which different Pokémon, moves, et cetera are tested and/or banned can have an impact on if something further down the line will also be broken. Case in point, an argument can be made for Zacian's Gen 8 iteration indirectly making Calyrex-Shadow more overwhelming than normal, since teams that already needed to prepare for the latter also needed to prepare for the former, which was next to impossible to do at times. In an alternate timeline where Zacian wasn't banned from Gen 8 Ubers, who knows? Maybe that would have been enough to push Calyrex-Shadow over the edge there, too. The world may never know.
The point I want to get across with this story is that I genuinely think Last Respects and Miraidon as a combination are unhealthy, but Miraidon itself isn't. Or at least, not as unhealthy as other AG names like Mega Rayquaza or pre-nerf Zacian were. Cut the Ubers council a bit of slack here- they were on a 50/50 split at one point as to whether Last Respects or Miraidon would be the first one to get suspect tested. I would imagine that the decision was a difficult one for them. They would have to try and account for both sides- would a Last Respects ban make Miraidon more manageable, or would a Miraidon ban make Last Respects more manageable? Either side of that coin would be met with complaints from the playerbase at large, but they can't just suspect both at the same time. My current opinion is that teams that have to over-prepare for Miraidon are unfortunately left extremely vulnerable to Last Respects strats as an unfortunate side effect, but that if Last Respects were to be tested now that this test has concluded, potentially hitting Last Respects with the banhammer means that teams that previously were designed with countering Last Respects teams in mind would now be much more open than they were before to dealing with Miraidon itself.
This idea of "one AG-worthy strategy making another AG strategy harder to deal with at the same time" appears to be the reason why it's (so far, anyway) so difficult, sometimes even impractical to have multiple different Pokémon get banned from Ubers within the same generation. Emphasis on different Pokémon- I'm not counting Zacian's two formes as separate Pokémon here. Another noticeable example of this can be found in the XY era of Gen 6, when complaints were going around about Xerneas as well as Mega Gengar. Gen 6 Xerneas never received the banhammer, and while I can't seem to find a consistent answer for Gen 6 Mega Gengar and if it got banned from Ubers, not only were both Pokémon eventually more manageable in ORAS, but you can make a legitimate argument that a Mega Gengar ban would have made Xerneas more manageable, too, since it's no longer around to try and trap Xerneas's best checks in that era, which is something it could try and do for Xerneas hyper offense teams against bulky Steels and other Ubers while Xerneas returns the favor against the Dark-Types that would threaten Mega Gengar.
(And before you say Pursuit, what happens when the Gengar is bluffing Gengarite, actually has a Colbur Berry, and all of a sudden Xerneas's teammate Mega Lucario or whatever just came in pretty much for free?)