If you do not include the hash of application.js in its filename then I think the main problem is whoever decided to use hashes for some scripts but not for others.
That being said, I don't use gulp and all that stuff. It seems to me that some people get so caught up in technology that they
1) Reinvent the wheel a million times. I admit that make has its short comings but I think a similarly general build tool is the way to go. Look into tup, they know what's up.
2) Don't notice that they are sitting atop a tower of abstractions and that their tower is starting to become unstable.
3) Are pulling in massive amounts of scripts as dependencies to build something that could've been implemented with little to no scripting at all, and with their high bandwith workstations and latest computers and devices they don't notice the fact that while they are trying to reduce load times (which by itself is a worthy goal) the browsers of their visitors are crashing because rendering these websites take more ram than is available on many devices. Jesus, fuck!
So that was a bit of a rant. Sorry about that, I guess.