Isn't the point of using Power Shot to proc your Rail Shot? How is that a waste if you get that many more Rail Shots?
The question is how many more Rail Shots do you actually get and what are they worth? I think you will be surprised by the answer....
First of all, there is an extremely narrow window of opportunity to use PowerShot effectively. You shouldn't just use it IF you see a stationary enemy who isn't paying attention to you. Since the main benefit of PowerShot is the possibility of a RailShot proc, you generally won't use PowerShot for a period of 6 seconds after using Unload. And then correspondingly it is almost pointless to use PowerShot if you used Unload 12 or more seconds ago, since your RailShot will be off CD anyway in two GCDs - which is less time on average than it would be to proc RailShot via PowerShot. So at best in a rotation sequence of 18-20 seconds, there might be a window of 6 seconds where PowerShot, even if it connects, makes sense to use. Right from the start the very rare circumstances when you can use Powershot just became even more rare.
And let's look at what happens if you do choose to use PowerShot. It takes an average of 2.22 casts of PowerShot in order to proc RailShot. Then you take your RailShot. Those 3.22 additional actions must displace 3.22 other actions in your rotation, which as shown above is already full. So you are not getting a "free" RailShot. Instead you are getting an additional RailShot at the cost of displacing an ability like ExplosiveDart or RocketPunch. And there is the additional cost of displacing 2.22 other actions for PowerShots that as noted above will fail to connect at a disturbingly regular pace. If there is even a 10% chance per PowerShot that it will not connect, the venture (using PS to proc RS) will generate a net negative impact on your damage output.
And that is the kicker. IF you spot a enemy who won't interrupt you, IF that target won't break LoS, IF that target won't get killed shortly or cc'ed shortly, IF you spy that target in that key 6 second window in your 18-20 second rotation sequence, IF you can afford to self root yourself and IF there is only a 5% chance another enemy will interrupt your 2-3 consecutive PowerShot casts, then and only then will you approximately break even on damage done. Doh. There's a reason why in all of my 700k and 800k damage matches, I've used PowerShot a total of.....ZERO times.
So Muzzle Fluting? Worthless for a Merc Pyro. Would rather have a point in Custom Enviro Suit. Which I do.