All good questions, and I don't know the answers, but I have some inklings.
As for #1 and #3:
I don't think Simms has a grudge against Tua, rather I think Simms really does believe in his ranking. Simms has been very vocal over the years that he likes strong armed QB's ... and Tua has just an average arm. Simms likes big QB's, and Tua is small ... like barely 6'0 small. Simms likes the very athletic QB's, and Tua has average athleticism for an NFL QB, so he will not be able to scramble like he did in college, and with our OL, he'll face a lot more pass rush, so he's gonna take a bunch of sacks. Simms also is one of the few evaluators who factor in the offense within which each QB plays, and the talent surrounding them. For instance, Oregon had by far the worst offensive scheme, Simms notes this, whereas most evaluators just blame Herbert. Alabama and LSU had by far the most talent around them, and Simms calls it out, but most evaluators just ignore all the top NFL draft picks surrounding those guys and say the QB is great. Jordan Love is the test case. He had a good surrounding cast and good offense his junior year, and did well. But when he had a bad offense and no surrounding talent as a senior, he played constant hero-ball and made bad decision after bad decision after bad decision. Simms notes this and blames some of those bad decisions on the need to do it all because there simply wasn't anyone else with talent enough to win the game on that team.
When you're talking about prospects, many evaluators place more weight on tools (arm strength, size, speed, intelligence, etc.) than the average fan. The scouts look at the upside, more than the current production. That's why so many scouts love Jordan Love ... he has those tools and upside. The person who checks those boxes the strongest is Justin Herbert, and that's Simms' man-crush. When you look at the mold of what Simms likes ... Tua doesn't stack up very well, so I'd guess his Tua ranking is honestly how he feels, and not a personal grudge.
As for #2:
Well, these days I think that's a valid concern for any media unfortunately, so there's probably some of that in there too. But comparatively to guys like Omar Kelly, no, Simms does not say things for clicks. He gets a tremendous amount of exposure because he's likable and connected. His "Unbuttoned" podcast is quite popular. Florio's Pro Football Talk gives him a platform to get noticed easily, and Simms's greatest strength as a pundit is that he's one of the most "connected" guys around the NFL. He knows everyone, and has a LOT of friends feeding him inside-advice. You don't see it a lot because he doesn't kiss and tell. But, rest assured, he's got more than a dozen personnel offices feeding him info at various stages of the evaluation process. So he's likable, gets exposure, not afraid to take a controversial stance, admits when he's wrong, willing to revise his rankings as guys prove they can or cannot play, and generally has proven to be a good evaluator. He doesn't 'need' to generate clicks, and that's probably why he doesn't seem to say a lot of those things that are inconsistent with his evaluation style like most click-bait guys do.