Even if they never intended to convey that BLU could solo their way through any content they weren't specifically locked out of, then I think that it was at least a reasonable assumption based on pre-release information that all BLU content---including spells---would be accessible through solo play. That the reverse is true seems like an inexplicable design flaw given the exclusion, not only from DF, but even solo content like squadrons. Given that BLU being a limited job was bound to aggravate those who wanted to main BLU through DF like any other job, it would have made much more sense to at least appease the more solo-oriented folks who enjoy crafting, squadrons, hunts, beast tribes, and other content where grouping is largely optional. BLU could even have made a lot of the open-world content relevant again---in fact, it almost did for approx 50% of the spell-learning process---but instead BLU seemingly only caters to an incredibly thin slice of the community who always have friends on hand to carry them through content. For the rest of us? It's now almost impossible to unlock the spells that are secured behind ex trials and the like... and yet Yoshi is happy with how it turned out? Seems like just a lot of wasted potential to me.