But the evidence fits my explanation as well as yours

No it does not. You assume that all such experiments are in vitro. You, for whatever reason, seem to completely ignore the millions of in vivo experiments on viral load and their correlation with sickness level. Now, even if you think it's all bullshit and all the conclusions are wrong, the measurements of viral load are not easily dismissed. This suggests that a virus can replicate quickly in vivo, even if it doesn't always do so.

I agree that a virus won't always replicate quickly. I am not arguing that. You seem to be saying it is ludicrous to assume that it ever can. I am asking you to show me any evidence to support such an assertion. There is a ton of evidence to the contrary. The link above shows such an experiment on viral load and sickness level. It is the first one I found that wasn't on Covid, since you firmly believe that one doesn't exist. There are literally millions more such experiments that have nothing to do with a "Petri dish." Unfortunately showing exactly how many there are is problematic because of all the noise with the covid stuff, and it seems you will reject that out of hand (without actually seeing what is being said). Nevertheless, here is a search that may provide some indication. Not all of those experiments are actually in vivo (one of the search parameters) but it is a start.

The immune system, absent in these experiments, intervenes long before microbes can reach this population level.

I spoke about this before. It's called a war of attrition. The immune system will absolutely intervene, but it will have various levels of effectiveness. Someone with a healthy immune system will respond quicker, possibly even killing off the virus before it can take hold and do actual tissue damage. Someone who has a long term immune response to that particular virus will also likely kill off the virus before it can get out of hand. If they have a partial long term immune response (anti-bodies to a variant that is "close enough") they may have a better chance of fighting it off, but reduced, so they might get "sick," but "not that sick." Someone without any of those things probably won't be able to fight it off and will get more sick. These are all possibilities, not "what will happen." What will happen is whatever will happen. Biology is complex, but that's not the point. You seem to admit that the war of attrition happens and that some people are better equipped to fight that war than others. However, you seem to be supposing that it can't happen as fast as literally every experiment ever performed suggests and that thinking that it can requires "suspending disbelief."

Where does the disbelief come from? It doesn't seem to come from any actual experience (experiment in this case), evidence, or even good argument that isn't based on "I don't believe it." It seems to come purely from desire. Your argument appears to be, at least in general, that because there is fuckery in science, that it is all fuckery. It is not all fuckery. Your argument seems to be that because scientists are all brainwashed with dogmatic beliefs that that makes them stupid. Those are not the same thing. They adhere to dogma without realizing, but they are not stupid. They have false beliefs. That doesn't make them incapable of doing good science (taking measurements and understanding what the measurements suggest), it just makes them more likely to come to false conclusions, but only if it runs into specific dogma. It's not all dogma.

While I agree that the arguments put forth by scientists should not be trusted, and even the measurements put forth by scientists should not be trusted, believing a priori that they are all wrong is not a path to the truth in honest investigation. On the contrary, it is necessary to, point by point, find actual flaws in the arguments and evidence presented. If you are not willing to look at all of the evidence in earnest, your arguments are based purely on belief. You seem to be forcing what evidence you do know about to fit your beliefs. If you are incapable of adjusting your beliefs based on the evidence, you can't be an honest investigator and instead will only adhere to your own dogma ad naseum.