Summoner needs a fix or a new reason to play it.

[Valence]

MCH does very good damage on its own in solo content relative to most jobs, and it is absolutely not a selfish dps. People want to act like raidwide mitigation is "needless", but the reality is that MCH is able to fix bad situations with its mitigation and dps profile being less dependent on raid buffs. It's a good job for fixing bad pulls, which is good and suitable for the fantasy of MCH.

Firstly I'm confused why solo content is mentioned and being discussed. Any job can clear solo content without breaking a sweat?

Second, in what world does MCH fix bad situations with its mitigation? What kind of content actually makes this a thing? I have played rphys across all varieties of content, from dungeons to ultimates, and never have I felt that the added rphys party support tools were actually necessary or would have saved a run (comparatively to any other role). Didn't stop me from using them because it's better than nothing, but then what?
Back in HW and SB? Yes. There was a lot less of those party tools which made them immediately more relevant instead of being drowned in a sea of mitigation (when there is only one healer party wide going for a specific raid wide, missing something like dismantle can change a lot of things, when there is already 5 mitigators up and running, then missing dismantle will not be felt a lot). On top of this mechanical clearance in most encounters was a lot less binary, with a lot less body checks and was less about "step in the wrong spot and wipe the raid": we definitely had this in savage+, but less so (especially in extremes for example) and this incidentally added a lot more weight behind party wide mitigation tools since it was a bit less about mechanics that didn't actually care much about this (DDR/oneshot), AND party resource management was a real deal and saving resources on MP, healing, etc, also had more weight.
We may also want to remember all that period of limbo during ShB up to mid EW where BRD and MCH only had ONE single party wide mitigation (Troubadour/Tactician), until SE eventually noticed that in comparison to DNC that had 3, it was maybe not the greatest look for them and turned Minne party wide and reintroduced Dismantle to MCH.

Let's not pretend that those tools do anything of big value here, unlike a raise for example. Even a MNK or RPR have mitigation tools that come close already. SMN probably heals ten times better than DNC, etc.