In physics there is 1) we know this is definitely wrong but it's useful and 2) this is very right so far and it's probably going to be wrong. I'm only a little bit joking. Now, I am not a physicist but I have been in a physics rabbit hole for a few months now.
The absolute best most experimentally verified theories we have are: general relativity and quantum mechanics. These are the pinnacle of physics. And they are incompatible with each other. So we know for sure that one is wrong. Or both are wrong.
String theory might be the resolution of that, making strings the most fundamental thing. But we've been working on it for 50 years with basically nothing to show for it so far. And there may be more beyond strings, who knows.
Of course there are many things in physics we can say with great confidence. But in terms of fundamental understanding there is ONLY "we now think that".
Regarding, "Quarks are the fundamental building blocks", do we actually think that? If so, why? I'm genuinely curious. Is it just because we haven't seen anything more fundamental? That would violate your "We now think that" qualifier - ie if that is the reason, the qualifier should be "We have NO reason to think that...".