Pretty sure the last rider to return to PCT level or above after any sort of doping sanction remains Simon Yates, which is 6.5 years ago. There's a case to be made that the riders you list got off too easily, but the fact that freaking Tramadol is now a death sentence for a career tells us that zero tolerance is going too far. And made even worse by the fact that a fair few of the team managers not willing to take him on have been caught with bigger violations.
Unless there's something going on we don't know about, of course.
I don't know if that's a decisive point because, to be honest, we don't have in the last years many cases of high or medium level riders who are caught on World Tour teams that even in normal conditions would deserve a place there.
The most well-known riders who have been caught since 2016 are Yates (WT rider), Sanchez, Brajkovic, Di Gregorio, Taborre, Pirazzi, Rosón, Preidler and Denifl. Apart from Yates, the first three were already retired or on a strong path of career decline, Taborre and Pirazzi were pro conti italian riders and I don't think Preidler and Denifl have already been cleared of their suspension. Roson is 30 already and imo, he didn't show much to deserve a place back in WT level after 4 years without racing.
But this is maybe a topic for another part of this forum. The thing is we don't have cases of high level riders been caught to test the team's zero tolerance policy. Of the previous list, only Yates deserved a place back on a WT team, and he is there.