This is not a bad advice overall, but I think that Citus has still a huge market to conquer before they go down this path.

Single PG node can handle easily 80k/s writes and reads and store up to 3TB of data safely. Wast majority of companies will never have to think about cluster as this is more than sufficient for most.

No matter if it's Citus or any other DB, horizontal scaling comes at cost and most companies should pay it. Citus helps to the ones that really have issues with performance beyond those levels (like us) and I think the Citus team is smartly targeting those kind of customers, at least for the time being.