I'm not an expert on either of those, but this is my take anyway:
Citus is distributed and afaik just eventually consistent, for a lot of folks that's simply not an option as their application relies on ACID compliance.
As far as I understand Hyda + DuckDB it is a higher level add-on onto postgres than timescale is. This is on the one hand nice since you can just put it into an existing database without any migration effort whatsoever.
But this also means they likely don't really interact with systems like the storage engine. For example Timescales deeper integration allows us to actually store the data differently on disk which allows for saving space via compression.
As far as I understand Hyda + DuckDB it is a higher level add-on onto postgres than timescale is. This is on the one hand nice since you can just put it into an existing database without any migration effort whatsoever. But this also means they likely don't really interact with systems like the storage engine. For example Timescales deeper integration allows us to actually store the data differently on disk which allows for saving space via compression.