WHM is my only level 50 job currently, and yes I did use thunder as I leveled. It was a nice extra tool to have, but not necessary by any means. It was nice to stack it in long fights if I had the extra time to do so. I see less of a use for blizzard II than I do for thunder, at least for me in level 50 content.

For those (like the OP) who are in the process of leveling it - you will find plenty of use of blizzard II in FATES. THM/BLM's spam it galore in many FATES for a reason. Use it to your advantage.