You literally described what Sony was doing for the whole Xbox One and Sony's plan for this gen. Conspiracy theory? Let's see.
- Fighting genre? Sony went after SF5 and it completely decimated fighting genre on Xbox. I do wonder how many fighting games skipped Xbox due to Sony's interference but we can't neither prove or disprove that. After all Xbox 360 was a very strong FGC platform, yet suddenly all of it was erased overnight.
- JRPG? Sony went after Final Fantasy, preventing Xbox from growing the community for JRPGs altogether as Xbox only got FF13-1-2-3 (unfortunately not great FF games) and FF15 (decent). Then we had Sega essentially being a first party for Sony the whole Xbox One gen with Yakuza and Persona games. So any chance for JRPG community to grow on Xbox was lost.
So during Xbox One era, Sony contributed to a full demise of two genres. Let's take a look at this gen. There were 2 genres that were still associated with Xbox - WRPGs and FPSs.
- The attempt to destroy FPS community on Xbox arguably started with Xbox One gen, but it was partially self inflicted due to Xbox not extending COD deal. At that time there was a rumor that COD deal was extended to the platform with the biggest market share (it was neither proved or disproved). There was also that Destiny deal with content being locked to PS for the full year (especially after Bungie leaving Xbox). Probably there were some other deals but I forgot at this point. And during this gen, Sony went hard after FPS games too with Deathloop and arguably Ghostwire.
- The crusade against WRPG started this gen. Recall the deals that Sony made (or tried to make). Sony tried to make a time exclusive deal regarding Starfield. They also went after KOTOR. Both games had a long history on Xbox. Would not be surprised if Sony went after some Bioware deals. Baldur's Gate? Probably nothing, but who knows. We also know from Imran Khan that Sony offered a lot of money for those deals.
But Microsoft woke up and realized that they were actually a huge company. The irony is that both Bethesda and ABK deals were only partially planned - Bethesda was dying (if their games did not flop one after another, the situation would be different) and ABK was imploding with its lawsuits and stock's crash. We can argue whose conspiracy theory is better - "Sony was killing Xbox", "Microsoft is killing Playstation", but in the end, personally, I can only play the world's smallest violin for Sony
Especially when you were describing such a dire situation with "developers supporting a platform with a bigger userbase more" etc. Which was exactly Xbox One.