from the sound of it there are 2 things probably happening...
first off, it sounds like you are trying to be strong at the beginning of the throw rather than the end. the real key to getting good snap is to focus your power into the rip. with the bent elbow, you treat the upper arm like a direct extension of the shoulder, that is, there should be no real lag time between the start of the shoulder and the movement of the upper arm. with a full reach back, players often have a slight delay as the upper arm lags behind the shoulder motion, but ideally, the upper arm should behave the same in both instances if you are going for golf d. you should be under control the entire time until the time immediately after the finish and so if you find your arm moving too fast, you probably aren't feeling the hit, meaning your armspeed is likely too high BEFORE it needs to be.
as for the difficulty with turning discs, the thing that often is a result of these drills are that players throw without off-axis torque on the disc. this is a good thing, as it is the method for throwing understable plastic as well as slower discs such as midranges/putters. if a player doesn't have the arm to throw a crush straight/flat, they will often still try to throw the crush straight/flat but then give a roll over to make the disc fly straight/flat. with a more controlled pull/finish, people often find themselves torque-less and thus the discs fly more stable, and imo, how they should.
once you get the timing down for the finish, you will find the disc will fly just as fast if not faster. it takes some work, but in the long run, you can incorporate this into whatever style of throw you choose and it will increase your power.