Go to ProfootballReference.comYou are making two different arguments. One argument of the Texans screwing up is very much true because while I wasn't sorry to see him leave anytime you have to pay a player to play for another team you've made a bad deal. As to the other argument on his performance there was nothing he did in 2019, or really before that, which impressed teams as clear by the fact that he almost went into the season unsigned.
They now have a section called Advanced stats.
Look at the stats for the entire Texans D last year and this year.
Then do the same for the Seahawks and the Titans.
You will see PD, FF, FR, QB hurries, QB Hits, sacks, TFLs.
There wasn't a single Texans D player that had/has the same effect as him; not to mention that JD has always been known as a stout run defender who can set the edge (which is also important against mobile QBs).