I don't think I'd fully agree with your first sentence. Pakistan reached #1 in the test rankings in 2017 and won the ICC CT that year. Really since the Ws got old it was a bumpy ride until about 2020 then pretty rapid decline since. I do agree about your assessment on players though - Younus definitely that last great (unless you include Misbah with his captaincy credentials).
A characteristic of Pakistan's success has been somehow getting alignment between one or two superstars, a few high very good players (the Azhars, Asads etc) and then whichever flash-in-the-pan guys are peaking at that particular moment. Still feel like Pakistan are producing plenty of that middle category but none of the first and, at present, none of the latter either.
When I mean slow decline, I mean that Pakistan essentially since the mid 80s under Imran and then the decade after him with Wasim Waqar was a top tier side, but then effectively for last 20 plus years Pakistan has been a mid tier side, with only brief flirtations at top tier status under Inzi and Misbah.
Under Inzi, Pakistan managed to draw against India away in 2005 when folks were certain we would lose, and then beat a strong England side at home in 2005, India again and SL away. We had the makings of a worldclass team with Inzi, Yousuf and Younis in batting and Shoaib and Asif as pacers but then both pacers ended up being out of the side for different reasons and we fell behind.
Yes, Pakistan reached no.1 in the test rankings briefly in 2016 but if I am being honest that wasnt that high quality a side to deserve it, it was more about Misbah making great use of resources to secure the UAE as a home base. I recall Ganguly mentioning the same thing. The same team was promptly after reaching no.1 beaten five tests in a row in Aus and NZ and returned to mid tier status.
And now Pakistan are a bottom tier side.
Winning the T20 WC in 2009 and the Champions Trophy in 2017 were flashes in the pan that can happen over a long period, akin to WI winning the Champions Trophy in 2004. India by comparison have any won a single ICC trophy the last decade but appeared in finals and knockouts far more often.
But yes what Pakistan lack are genuinely worldclass players with long enough careers as you said to be the foundation of the team. In particular, worldclass pacers.