Take it from a guy who has watched almost every spell bowled by both bowlers in their entire career. You are wrong on pretty much every point.
1) Taskin is only a yard quicker than Mustafiz by BOTH average pace and max pace. Taskin generally averages 85 mph, Mustafiz 80-82 and that too because he bowls a lot of slower deliveries. His true average would be arpund 83 mph. You tell me what the difference between 85 and 83 is. 2 if I recall correctly. In terms of top pace, Taskin's fastest speed was 148 kph in the Asia Cup match vs Pakistan. Fizz clocked 144 in the IPL, and apart from that has clocked 143 vs SL in the first Test and also 143 vs South Africa in Chittagong. Again the difference is only 4-5 kph.
2) Mustafiz can swing the new ball on occaision as he did vs SL. Taskin has absolutely zero swing, none at all. They can both reverse the ball when the conditions allow it. Taskin does get the ball to jag off the seam, and also gets more bounce than you would expect from a bowler who is only 6'2" tall.
3) There is no evidence to suggest Taskin's work ethic is poor. In fact, given the injury issues he's had and the fact that he's a gym rat, its more likely he takes his job quite seriously.
You can rate Mohammad Sami ahead of both of them, why stop at Hasan or Lahiru Kumara. But frankly, you need to go and learn about fast bowling or at least watch the guys you speak of if you want to prevent the bakwas thats hemorrhaging from your ears.