I have the 8-element Super-Takumar 50 f/1.4, and it would be criminal to call it soft. Even though the later ones have a change to the optical design, I don’t think anyone accuses them of being soft (but certainly very think DoF wide open). Please direct us to the YouTuber who has made these allegations so the Pentax Army can be sent after them
More constructively, then Google machine suggests that the 90D has focus peaking. I would try focusing using that rather than the OVF to assess focus and sharpness. I do concur with others that this particular lens copy appears to have issues, perhaps from a botched repair (or modification attempt), but I always thing that live view focus peaking is extremely useful for focusing these older lenses, especially at wide apertures. (For your tests, I’d say to stop down to f/4 or thereabouts and then focus in live view with focus peaking.)