Which contradicts your statement of appreciation.
This product, even in its current state was a 6 year development time. There are numerous version of an FMC and even systems in 737s, so while I won't comment on everything you listed, I will leave it to @Litjan to do that.
I could not disagree with you more about the price and value of the product. Jan specifically, as a longtime Captain in the 737 Classic worked tirelessly on the systems simulation, and from the FMC standpoint, crucial/vital parts to what were used in everyday flight were implemented. Accordingly, IXEG was also very candid in what was not simulated, and has always been (albeit, in our eyes non-crucial).
VNAV is a debatable topic. I think we'll all agree that it's the sore point that needs to be worked out next for the team. That said, simulation enthusiasts tend to have this dependency on VNAV that is really not so present in the real world. That may be due to the fact we do one-man pilot operations (I'm making up excuses for why a simmer depends on it more that an real world pilot) in our cockpits, but in the real world, VNAV was not such a heavily used item for Jan.
I'm sure he'll reply to your other points when he can. It sounded to me like you may have a wrong perception about how certain things are done, irrespective of the FCOM reading you're doing. Jan can further clarify that for you.
This is an indication of you likely not knowing anything about "unoptimized programming". It has nothing to do with that at all.
In Gizmo's tool tray menu you'll find a Garbage Collector icon. Utilize that and adjust some values to get a more favorable, smooth experience. I'd start with a value of something like 500.