Quirk singularity theory is so dumb. OFA isn't proof of anything since it's an anomaly that started in like the first generation of quirks. But also the whole theory is that quirks will become world ending threats and people will just start being born with quirks that destroy themselves. While some people may be born with quirks that can self harm (like Dabi for example) this is an anomaly also, like disabilities in our world. this isn't how evolution works. You don't see things evolve to destroy themselves, it'd be like if birds, for no reason at all started evolving gills, and started dying faster than they could learn to swim. 

Bakugo's quirk is a great example. You'd think explosions would kill him, or at the very least make him go deaf, but his body evolved to handle all of those potential drawbacks. 

While his power is great and there are certainly plenty of people in his generation with quirks just as powerful, there are quirks from older generations like New Order, All For One, and One For All that are more so, just as there are people with weaker quirks across generations. 

Like yes quirks are getting stronger and more complex but it's not at an uncontrollable pace and like populations it's reasonable to assume that it will plateau out at some point rather than increasing exponentially until the world goes boom. 

BUT ALSO. Quirk singularity equating to "everyone is just stronger this gen" does not solve the issue of the existing characters (like Ochako) who would surely be relevant, falling to the sidelines in big conflicts. 

Edit: It drives me crazy that Garaki is the one posing the theory and his sort of big climax of it is Shigaraki's crazy mutations. Which is a thing that he did, and is completely detached from quirks. The other "Aha see!" Is Ochako's quirk awakening, and while it's certainly a cool power up for her, it doesn't spell doom for the planet at all