Rez loss from cropping VS longer FL

So I have a basic question, maybe you know from experience or maybe just have a guess, both are welcome and appreciated. My question is, theoretically, would cropping a good 200mm FOV from a lens like the tamron 70-200 end up better or worse than the 300 end of the pentax 55-300? (in terms of sharpness).

Assuming all other things are equal like focusing and iso, and if both lenses were in their sweet spot with apertures (F4/F8 maybe), could the pentax @300mm be better than the tamron @200mm cropped to 300 FOV? For things like birding, I would be content with a 300mm or so FOV (could get a tc if I needed more), but the tamron is so sharp I was wondering if i would be better off cropping it. I am not paying attention to cost because the tamron could double as my portrait lens @70, effectively filling two roles for me.

I guess the question is, how much does cropping in 100mm dissolve the resolution? I am pulling for the tamron as it is also better for low light tele shooting, but I hate sacrificing sharpness in the process.