An absolute false premise to justify a vision and a corporate decision to go a certain route. Basically Fear mongering with a foreign enemy as usual being the evil prop lurking in the shadows - works every time on many sheep - comes from politics - psycological trap for the mind.
PlayStation will survive just like it survived during the PS3 era without a big FPS, and all their failures in this regard trying to chase COD, Battlefield and Halo.... they'll survive again. Their salvation was cinematic, AAA, high quality single-player games - a niche overlooked and unexploited while everyone was after the next COD. "Without a big shooter you can't survive! Ha ha Uncharted!"
PlayStation will survive just like it survived during the PS4 era where the nascent GAAS model actually took off, not in the PS5 generation. It's a transient fad.
No one is saying SIE can not try to get their feet wet GAAS wise with some projects here or there but when the allocation of resources goes 50/50 or greater in favor of GAAS vs. everything else that is not the way to go. They already pocketed Bungie, with Destiny, one of the TOP GAAS games on the market + their future GAAS projects. Bungie is now in house. Moreover they profit the most with third-party royalties on any GAAS game in the industry, including the biggest of them all - Fornite.
Not only is it a crazy idea to put half of your eggs on the GAAS basket, it's guaranteed failure on a massive, billions of dollars scale and a disaster in the making. Failures will be felt and hard and SIE is not playing to their strengths. This is not an organic push, this is a rush to cash in. It would be even more counter productive if in the process of getting into this fad, they miss the next evolution of the "next hot thing" (the next thing after GAAS). Sony should strive to be at the vanguard trying to innovate and be a trendsetter exploring various ideas, finding new niches, not in effect being a trend follower trying to squeeze one IP on a crowded market with very well established players. An insane GAAS push is myopic creative destruction on a big scale - like hanging by a thread - the thread being a high risk bet that you may cash 1 GAAS game in and cover the graveyard of failures left behind. The amount of resources that they're allocating to this push, and the opportunity cost of that money being allocated elsewhere into safer or more manageable bets is big not to mention also potentially counter-productive risk taking.
Moreover, given the potential for sequential failures (several duds in succession) in such a tricky market, SIE is setting themselves up exactly for what OP's premise intends to prevent (the supposed competitor threat that will consume PS unless you do X (in this case GAAS)). All big publishers have in some way or another struggled mightily in this regard, Warner, Square, Ubisoft/ EA, even ABK (who happens to be reduced to a COD churning machine).
Suicide Squad (???) - def not look too hot.
Halo Infinite (marquee franchise dead).
Overwatch 2 on shaky ground
+ more and many more to come.
Genshin Impact (nice niche find).
Final Fantasy XIV
Rainbow Six Siege
Mostly shooters. Always the common trend. Moreover to support successful GAAS, studios blow up in size. Yet you never know when the plug is going to be pulled on your game because it became Yesterday's news. No game lasts forever and there are many studios now riding high on this GAAS wagon who will see bloody days when their audience shifts to something else. Their inflated workforce will not be manageable on crumbs and you better hope you saved enough for that rainy day.
Reminds me of: "Nintendo must go mobile." "MARIO everywhere - multiplat." We know how that ended. The Switch, their most successful, profit wise, console to date. Market share/footprint wise that still belongs to the Wii + DS combo era.
If you want a justification for going GAAS full steam ahead you will always find reasons and come up with them. But likewise you can come up with a justification for a vision where GAAS is non-existant, minimal or where your exposure is not highly significant in your overall portfolio. It's called a vision - not all visions pan out, not all ideas are good, not all trends fit on one sized shoe.
Fear mongering for conformity to the current vision of PS leadership is absolutely not needed on forums and boards by normal fans. It's a disservice to discourse. Nor is your conformity required for you to continue to be an obsessed fan of the brand - I see a lot of posters struggle with this: associating "brand allegiance" with conformity to leadership direction - crazy but it's a human thing. What's left of the Xbox fanbase is perfect case study but most obviously you'll find it in the 150m or so gamers on the PS ecosystem - even higher numerically speaking.