There's a lot of literal bullshit to dispel here.
First, the whole bison vs. cow argument is bunk for a variety of reasons. The diet that roaming bison ate is very different that the beef and dairy cattle eat today. Also, they didn't typically shit in large pools given that they were not animals that we're penned in to the same geographical location and roamed, often over many, many miles throughout the year.
Second, you're looking solely at North America. Cattle "production" is truly worldwide at this point, with beef and dairy cattle farms in many far off places where the animals are not native, and the true reporting of their numbers is grossly under-reported.
And, the whole goddamn thing about fungi is just.. I don't even know where to start with that. The amount of food created to feed cattle is staggering, and without that need in the first place, then the fungi wouldn't need to metabolize and emit methane, even though all of this is just some kind of insane babble. The methane comes from huge pools of manure that can, and more likely is not, properly and sustainably dealt with. There are blighted areas in the US alone where large cattle companies have simply abandoned the areas due to health concerns.
Here's the thing about methane though, when you generate an enormous amount of it, year over year, the cumulative effects of it cooling the planet (you know, melting glaciers, raising sea temperatures) does not really give a damn about the half-life of atmospheric methane. Once those effects set in, they're self-perpetuating and continuing to feed into the same root causes only makes it more difficult to resolve.
Finally, if you think that beef filled with GMO corn is some kind of magical health / nutrition goal post, well, there's nothing I could possibly say to counteract the sheer inanity of that position.
I think Beyond Beef is fine. I don't eat it for "health" reasons, and anyone who eats mass produced ground beef for "health" reasons is just straight up lying to themselves. All of these are comfort foods that we can all sustainbly live without. The decision is whether the slight taste difference is worth the absolutely terrible cost to the environment, and the devastating cost associated with the mass slaughter of sentient animals.