You seem to have a lot of problems with that game :).
As for spike damage, most people struggle with it, especially those that think Reyn becomes useless later.
Some characters have skills which reduce Spike damage, which becomes invaluable against some UM spiders, behemoths and mékons, as some types of these inflict Spike damage when you topple them.
Also, some early quests and collection completion give you early spike damage reducing gems which allow you to tackle the UM without problems. Taking 100 % of Spike damage will just destroy the faster dealing damage characters in the early game. In the end game, when you get the top level VI gems, it will be easier.
IIRC, there's nothing you can do against Arts Seal, but that's the moment you can choose to build your talent art gauge. But there are anti-Bind gems.







