So, if I can get this straight...
The 921 rocket is essentially a "CZ-5 Heavy", an offshoot project meant to fast-track CLEP's manned lunar missions, and in many ways comparable to the crewed SLS Block 1. Its design consisting of 3 CZ-5 cores heavily suggests that it's meant to use as much off-the-shelf technology as possible. We can expect this launch vehicle to debut sooner than 2030 which is when the CZ-9 is expected to fly, consistent with photos that the core structures are already in testing.
The CZ-9 is more of a long-term venture designed to haul heavy cargo to lunar orbit and beyond and will not be man-rated. I expect this project to be more on the backburner, with the 921 project stealing the spotlight (and with that most of their engineering talent). In other words, it's the CNSA equivalent of the SLS Block 2 and will likely fly in the same time frame (or maybe later since delays seem to be inevitable with the Chinese space program).
Sounds about right?
So far the Chinese seem to be emulating the SLS program down to a tee.
I guess by offshoot and fast-track you meant alternative. And your understanding is a two step approach, first 921 multiple launches to put man on the moon, followed by larger scale landing using CZ-9. My answer is, maybe or maybe not. So far I have not seen any paper suggesting this is the case.
Here is some background information.
In a paper by Long Lehao (2010), there was two phases to land man on the moon. Phase one is multiple launches without CZ-9. Phase two is crew rocket plus CZ-9. In one of the alternatives of phase one, there was even CZ-2F crew rocket involved, with two CZ-5s being the cargo rockets. Phase two is CZ-5DY crew plus CZ-9 cargo. This is the paper I have read years ago. All these plans require earth orbit rendezvous (EOR).
However another paper (2009), EOR was deemed too complicated and risk of total mission failure is too high due to the earth orbit waiting and docking. This paper basically made the same conclusion as Apollo which also proposed and killed the idea of EOR. This is why I kept objecting the idea of multiple launches of smaller rockets in place of CZ-9 class.
It is worth to note that Long Lehao's paper is about the overall idea of moon mission, not in detailed study of various approach. The 2009 paper is the outcome of sub-study into details. So it should be taken more seriously.
I believe that based on the study of this paper, CNSA has committed to LOR (lunar Orbit Rendezous) which Apollo used. But there is a difference. Aopllo's LOR is only about the docking of ascent stage and the returning modules, one LOR. CNSA's plan has the docking of crew with the landing combo before the landing, two LOR. CNSA's approach will significantly increase the total mass to TLI 75t or more, compared to APOLLO's 50t.
In this new approach, CZ-5DY was deemed two light to send crew module to lunar orbit, so it is replaced by 921.
Both papers have envisioned both small scale and large scale landing. However it is worth noting the conclusion of the 2009 paper.
It says "we can conduct small scale (4 or 3 launches), OR go straight to large scale (2 launches, crew + cargo)."
It seems that by that time in 2009, both approaches are on the table, but there is no decision of having the small scale as first step. It could be a large scale as the first step too.
Regardless which approach, 921 is not alternative to CZ-9, it is the crew carrier which may act as a cargo carrier in place of CZ-9 IF 921 is much faster in progress than CZ-9. However, I doubt it will be faster enough to warrant a small scale approach, we are looking at between 2025(921 earliest) and 2030 (CZ-9). Considering 921 is manned rocket, it will need multiple un-crewed launches (3 to 4) before sending man to the moon, that will put its earliest manned mission to 2028.
One the one hand, 921 can be seen as a fast-track alternative before CZ-9 is ready, or we can equally say that "multiple 921 launches" is a backup in case of CZ-9 delay.
