Yeah, as I say it's not specifically about Mahmood, more just a general point.
I've coached some very exciting young bowlers at county level, but counties get wary of playing them because they're erratic. They'd rather pick the 33 year old journeyman who bowls wicket to wicket, keeps it tight and and picks up LBWs than the 20 year old who can bowl 88mph but will go for a few runs. That's perfectly understandable from the county's perspective of course. What usually happens though, is the bowler modifies their bowling in order to get more chances in county cricket, they lose a bit of pace, start pitching it up more, become more reliable and so start playing more. Mission accomplished. But now they're no longer a hot prospect because the England team isn't looking for 80mph steady eddies. Then we go to Australia, get hammered, and everyone complains that our bowlers are too slow and all the same.