All you say is true. I would suggest that anyone, manufacturer or other, would take these sorts of future production list in their real world context. At the rate BUM and GerMan produce sets many could be 5 or more years down the line. If Strelets decided to make some Egyptian campaign figures they would probably be able to produce and sell the whole batch before GerMan produced anything.
Another aspect is that such promises could encourage others to produce. People often say they would be more interested in subject X if a good range was available. Well if you know IMEX will be making some French/Indian War figures then that seems like encouragement for you to make matching sets. If you aim to deliver in 12 months or so then hopefully that won't be too far away from whenever IMEX deliver, then everyone is happy. Although Zvezda are surely never going to cover GNW like Strelets, the fact that they are contributing should be a boost for Strelets, whose figures will still be needed in large amounts for any proper game or diorama of that war.
Finally, I want to see my hobby grow. I don't want to deter companies from making figures just because they cant or wont produce large numbers each year. Gulliver only ever made 1 set, but in my view the hobby is a better one with that set than without, so to my mind all are welcome, quick or slow!