Using Objection for more than a year in a medium sized ERP project. Not bad, but for sure on the next project I will use directly knex as querybuilder (with no ORM part). The ORM part that Objection add to knex don't bring much value and add a layer of complexity. The only functionality that I would miss would be the graph operations (withGraphFetched, upsertGraph, ecc.) but writing them in SQL (using KNEX) would not be a great problem.
Have you considered a tagged template literal sql builder, such as https://github.com/blakeembrey/sql-template-tag ?
Keeps the SQL syntax so less to learn, but still offers parametrized queries.