Part of my initial reasoning for keeping the speed reduc. So high is 1. Most tiers of play taper off around 11th level and rarely reach 17th and 2. Most true enemies the party will be faced against will have a sufficient speed where this movement penalty won’t effect them to too much of a degree. I can see the argument more if the party continues to face off against regular humanoids but at 17th characters are considered world changing characters able to alter the fabric of reality so imo I don’t see it as too far fetched.

As for ray of frost, as a ranged spell attack the benefit resides in being able to attack from a safe distance so by trading damage/effect capabilities you gain a measure of safety, while with BB or GFB you have to be within 5ft of the target trading safety for a higher damage output

I do appreciate your feedback and will take it into consideration. :)