Sprinkler has not really been nerfed, it's been rebalanced with a new purpose just like a few of the weapons and other subs. For the first 6 seconds it spits out ink a lot faster than it does in Splatoon 1, then it slows down to around the same sort of speed as it had in Splatoon 1, then around 12 seconds from the first slow down it goes to super slow speed and you need to throw a new one. Look at the original Sprinkler, for 80% of your ink tank you could throw a sub with infinite ink, constantly covering over an area provided the enemy don't kill it. Combine that with the fact there are plenty of places to put a Sprinkler out of reach of practically every weapon in the game and you had a really cheese way of keeping map control as long as you stayed alive.
Now Sprinkler is there to provide a quick burst of turf in the area it was thrown to, can be used as a quick distraction still and it will carry on contributing to fast special building. These changes have been done in mind to prevent people finding spots on these maps to put them out of reach again for easy infinite inking. Besides, it takes around 18 seconds for it to become flat out useless, how long is the lifespan of your average Sprinkler? It most likely isn't 18 seconds every time, especially when you just want quick turf to take.
Want some final evidence that it isn't nerfed to the ground? Take a look at this image:
That's the Turf coverage you get with it in the first 6 seconds of rapid fire spray. That's basically the maximum amount of turf you'll ever get with it, only having the gaps fill in afterwards and by that point someone will have killed it or you've thrown another one in a different area of the map (that's how I usually utilise Sprinklers). In this new re-purposed form the devs have given us a great inking sub that wants to be moved around as much as possible to capitalise on that inking capability. Yes the ink cost is high, and it might not be the best fit for the Heavy Splatling, but Walls take too long to open and unless Bubble Blower can be easily exploited by the Heavy, I would much rather play this variant due to the crazy ink output which helps keep map control under check. Just my thoughts on it, we'll see how the devs decide to change the Sprinkler in the coming updates should they feel it needs a nerf or buff. I don't know how effective Sub Power Up is, but I don't think it's worth it due to how short the lifespan of Sprinklers usually are, but this change is to stop infinite easy turf for Splat Zones and Turf Wars.
