Not sure about expertise, but I was the one always backed Abbas for this WC only - AND I WILL stick to that.
One reason being lack of options, more or less there is a brigade of 130K ish pacers, and most of them are left-armers with very little skill, intelligence and heart. They are good at slanting the ball across right handers which looks "threatening" in tv, but effectively PAK new ball attack is statistically well, well below minnows like Bangladesh ..... and if you take out that all important ZIM tour, where Faheem Ashraf has 9 wickets at 2.56 economy & 7.5 average, this stats might go below minnow level.
This guy Abbas knows how to use new ball, has the bowling intelligence of setting up batsmen and he can bowl in channel - at least won't chase batsman 2 metres wide & one metre high. Abbas might go for 6 boundaries in an over, but be sure that all 6 will need to penetrate fielding cordon - he won't bowl short when Captain has pushed long on/off out and brought 3rd man, fine leg in circle; he won't bowl a leg side wide with 6-3 field, he won't bowl wide half volley when cover, mid off & extra cover are posted to stop singles - that's bowling intelligence, lack of which sometimes can cost you 29 runs in an over, even at 140K pace.
Even on 350 per English tracks, ball will swing/seem for first few overs in June, and a bowler intelligent enough to make batsmen play at new ball will trouble modern top order batsmen in PP - for a sanity check, you can take a look at the stats of tundler Mashrafee's opening spell at 120Km, bowled on one knee .... not to mention Indian opening bowlers whom I can't recall when last time went wicket less in PP, may be 2017 CT Final.....
Second reason is unreal expectation - PAK fans have to measure their expectation according to the level of their players outside PSL. PAK top order can't do what Aussie top 3 did in last 2 games; that doesn't mean Abbas is rubbish .... you have to give a chance to other possibility as well - may be Abbas was bowling to proper batsmen on an absolute belter with short boundaries, whereas Aussie opening pacers were bowling to a pair who would struggle to make minnow Bangladesh's bench - statistical comparison isn't fair here. Even on absolute 180 adverse condition for his type of bowling, Abbas was by far the best PAK pacer in 1st game (actually best pacer in the game combined sides) and it's a bit rich to question "expertise" for suggesting a bowler going for 10-0-44-1 figures on debut, for a fan whose team conceded 282 for 2 in 49 overs in that very innings.
Afridi gives an unique dimension - height, in a bowling unit, embarrassingly challenged vertically; Hasan gives another dimension - middle over bowling, he was almost like pace version of Warne or Murali in CT; Hasnain or Wahab gives another dimension - pace .... Faheem gives another dimension as well - phast bowling all-rounder, who bowls at 130K and bats at 6 like No. 10. Apart from that, these Amir, JK, Shinwari, Hamza, Rahat..... are more or less same, and Amir is one eyed prince among blinds - that makes Abbas indeed a good prospect for the squad of a WC in UK, in June - hardly matters what he does in UAE in late March under lights.