This class looks pretty great. I like the prepared invocation spin on the class. The only thing I really think needs changing is: if they are a class about learning and using all kinds of esoteric lore, then why do they have a set list? I say, list only new invocations introduced with the dabbler and say they can learn any invocation.
The dabbler's list already most of the warlock and dragonfire adept invocations. For the most part, the invocations that aren't already on the dabbler list were either redundant (the additional flight invocations), nonsensical (the invocations that modified either eldritch blasts or breath weapons), or that I didn't wish to include for mechanical reasons (such as the various dispel magic invocations).
If brute force isn't working, that just means you're not using enough of it.
When in doubt, set something on fire. If not in doubt, set something on fire anyway.