I don't agree with all your points. I don't think the remark about the Skill Swap Trevenant is necessary or adds much seeing as keeping chains going against most pokémon is fairly straightforward even without that. I'd only advise to actually go through that trouble for chaining pokémon with a very low calling rate as they might not successfully call another before running out of PP (Sharpedo for instance). But in the vast majority of cases you can just switch to a fresher pokémon and KO the older one every ten or so summons.
I also believe that if you ditch IVs (which I actually support), you should also ditch the influence of natures on stats. I think natures, perhaps even more so than IVs (which can at least be hyper trained), limit options, especially when considering limited pokémon. I could only get a single Kyogre in my Ultra Sun file through the 2018 legends event. I settled with soft-resetting for Modest, which disqualifies me from adapting my strategy later to for example a Trick Room-focused Kyogre which would run Quiet, or maybe one that's a bit faster and would run Timid. With regular pokémon I can simply breed another one with the nature I want, but with legendaries I can't. I was considering trying a special Silvally, only to find out that all my Silvally and Type: Null don't have the right nature to support such a strategy. And especially at the higher stat numbers with EV investment natures have a quantitatively larger impact than IVs do. Keep the influence of natures on pokémon tastes (like which berries confuse them, which pokéblocks and malasada's they like, etc), and perhaps give different natures different animations in refresh and battle to differentiate them in personality rather than in battling proficiency.
Also, why is this in the Sword and Shield section?