Pakistan plays few tests is absolute nonsense excuse for this.
Younis khan has 10,000+ runs and a mediocre batsmen like Asad Shafiq has played 75 tests in his career, there is no reason for a fast bowler not to take 200 wickets in this era for a top 8 team. Windies recently had Kemar Roach getting to 200 wickets.
It takes about 50-60 tests to take 200 wickets and this is literally not much. Yes, it's harder for Pakistan, SA and NZ to get to 400 wickets today but 200-300 is very much reachable for all.
Neil Wagner has been playing from not too long and has already reached 200 wickets so a benchmark of 200 wickets completely makes sense. As for wickets getting shared that is again wrong opinion, Starc, Cummins and Hazelwood all will go on and have 200+ wickets by the time they retire. Same for Steyn, Philander and Morkel and Boult/Southee/Wagner. All these teams had their wickets getting shared.