Sequelize was a huge drop in efficiency for me any my team. As soon as you go outside of the typical select-where statements, it completely falls apart. I spent hours manipulating that horrible "almost-SQL" syntax to get it to spit out the query I wanted, and often I would just give up and fall back to using a raw query. Yeah, it's great that you can use raw queries when you need, but I soon realized that I almost always wanted to use them.
I switched to KnexJS which has syntax that is practically one-to-one with SQL and have had very few problems since then. Generated queries are much more predictable and easy to write, and it forces you to improve your SQL skills. I view that as a good thing.