My general take is that while the idea of composability is good, the implementations of these things are just frankly not of high quality. Velox/Acero in particular are all plagued by what I've come to call "Java syndrome", where everything is written as idiomatic Java but with C++ syntax. Virtual methods, std::shared_ptr galore (in lieu of garbage collection), random heap allocations, etc. As a result these systems tend to be bloated and significantly slower than they need to be.

DuckDB is good though, and I predict its quality of implementation will keep "monolithic databases" relevant for a while longer.