You get the advantage of choosing any of those libraries/tools that make up an application (e.g. choosing a router library that makes sense to you [or the team] and/or for your app). Thus, intrinsically the learning curve is much more digestible than grokking why certain parts of a monolithic framework (e.g. Angular) are designed the way they are.
However, that may also lead to being kind of paralyzed by the amount of choice you have. I know I'm not alone in sometimes preferring to have most of the[1] choices already made for me. (Especially when I'm not really a domain expert nor interested in trying to keep up with all the newest goings-on in the area.)
