You might use that word, "bust" too liberally. By such a metric about a quarter or more players in the NFL are busts.
Then again, here's the thing with Tua. He's entering the 5th year on his rookie deal. There's talk right now about how the Dolphins are going to sign him to a massive extension, something along the lines of Justin Herbert, as he is their guy. Something around $45m a year, with at least $30m of that guaranteed (depending on how that is structured), despite some impressive games, and very impressive throws, I have yet to see any indication to me Tua is worth that much (very comparative term, NONE of these guys are "worth" this much cash. The world's top neurosurgeon likely isn't "worth" $50m a year, nor does he/she earn that).
Let me give you an example, last year Roquan Smith signed a huge deal with Baltimore. Arguably the best LB in the NFL, maybe even a top 10 defensive player in the entire league. His pay? $13m this year, though there are bonuses, and his full contract is a nice $60m guaranteed over 5 years. Pretty good pay, really.
So, is Tua worth TRIPLE what Roquan Smith is? Ask me that about Patrick Mahomes? Sure! Lamar Jackson? Probably (if he can stay healthy). But Tua? Who in their right mind thinks so? Well, it's pretty likely Miami will pay him like he is, or close to it.
And it's not like Tua is stuck on a crappy team, having to elevate guys around him. His offense is stacked! So, he fails to deliver on that and take Miami deep into the playoffs in the next couple years, you might as well call him a bust.