Using the Creation Kit I made a few quick tweaks to how master spells work. The first issue I had with the master spells was not being able to move. The easiest way to fix that was to make it the spells cast with one hand. The next issue I had was with cast time so that has been reduced from three seconds to one second. You are still able to to interrupted in that second. Lastly I made sure that all master spells had the ability to be dual cast. Ultimately, spells can be cast from either hand or dual cast, both while moving, and have an interruptible one second charge time.
For master level scrolls the same changes were made with the exception that they are unable to be dual cast even with the correct perks.
There are similar mods already out there but were for the older version of Skyrim or included extra things that I disliked. There still is good balance but these spells are now useful. If you have gotten to the point where you can use these spells you deserve their actual power.
Disclaimer: Lightning Storm is super bright with sustained casting and blizzard causes motion sickness with or without this mod.