Neither Sarfy or Rizwan are even decent WK - first filter is that, they snatch the ball, doesn't glove it. It was mid 90s that stamp Micro was installed & I never hard Latif gathering balls, even from Sohaib. Now, even without stamp micro, spectators will hear Sarfy or Rizwan snatching the ball of Imad

from stands.
Second filter is, Rizwan is extremely fit, perfect body shape, weight & naturally gifted athlete, so his reflexes are better & his body movement is faster; besides, he is few years younger. WK in AUS is easiest (If take WK as easy job), compared to Asia o UK where ball spins & swings late - hence Rizwan is looking decent - he'll drop half of the balls in UK, if it starts to wobble in air. All this actually tells what is Sarfu keeping.
Sarfraz seems to do better against pacers, because most posters don't know how to judge a WK. Last week, Mushi bunked keeping & Imrul took charge - and he collected 6 catches in one innings (& 30 bye/wides in 180 overs

. Sarfu doesn't even attempt anything outside regulation - AND, he stands at least 2 yards behind for a perfect spot on any given wicket - hence many balls reach in 1st bounce to him. Ideal distance for a WK is when the ball is flat in trajectory, that's, it has finished the rise & now would go downwards (Knott used to stand in a spot that he could gather it on the rise - that's from John Snow, Jeff Arnold & Bob Willis; but no one is Allen Knott - his reflex was sharp & gather was silky smooth - stood on stamp for medium pacers).
Anyone can check - 50% balls Sarfy gathers with his fingers pointing ground - means he is standing far away - which affects PAK's slip catting as well. MoHa is a genius, one & only 1st Slip fielder in history with 50/50 sort of stats, but others in PAK slip cordon are decent, YK is far better than decent - but, they stand at least 2 yards behind - this alignment is done by WK, ideally 2nd slip stands parallel to WK - Sarfy stands too far away hence, we have seen too many 1st bounced ball at slips. And, he never covers 1st slip.
3rd - the best WK's I have seen actually gathers leg side balls in their inner gloves with a twisted body - that's if he misses, there is a chance that it rebounds of outer gloves or thigh to slip or short leg. For that, you need good anticipation, soft, nimble hands, extremely flexible waste, strong hamstring & quick feet - so that you can move outside the line of the ball. Most of the leg side balls Sarfy even can't touch with his left hand - because his structure is bottom heavy, low centre of gravity which can't move on toes & for his height, he is at least 10-12 KG over weight for a WK - NO WK, standing on heels will ever be able to take anything on leg side - Sarfy keeps against spinners with his body weight on heels. I can categorically tell that, with a months' training, at this age Latif will keep better than these two by some margin - because, his technique was sound, body shape was perfect for a WK & his anticipation was out standing - no WK can keep better than Latif against reverse swing - he hardly gave any bye to WW at their prime; Sarfy would have scored a 50 in every Test innings that crossed 100 overs.
PAK's best WK in recent years that I had seen few times in youtube was Jamal Anwar, by some margin. And, his structure is perfect for a WK. Sadly, he is not that good with bat & wasn't part of the stability philosophy. Even 2nd Akmal is not a good WK, but he is better than these 2.
There is one short term solution - Sarfu has to be trusted as WK & hope that he somehow manages a reasonable stats till 2019 WC (BUT not as Captain - he'll put 10KG more if he is made Captain). The only way, based on watching Rizwan in recent times after few weeks with Rixon is that - bring 4/5 genuine U23 WKs with good batting potential & train them under Rixon. He can chalk out the training schedule & improvement scopes for individuals - those who are hungry enough, will find their own way to apply Rixon's suggestions. One doesn't need 5 WKs - just 1 from such 10/12 boys is enough for a decade - that U19 WC kid is a fantastic prospect for a modern batting WK - very good batsman & a decent WK, in perfect shape & structure to invest on keeping; he should be immediately called as a back-up & made to tour with team under Rixon.