Now you are taking issue with concurrancy. The ones that are flying right now we're built to an earlier development standard. While safe for flight and limited combat use, they are not a fully baked final model.
In older projects, a development standard was chosen and a large batch of fighters were built to that standard. Find out that it can't handle new weapon X? Tough tamales! You're getting 150 of them that way. Now, they start low rate production to a designated development standard and build a small batch of them and use them for a bit. What they learn is then applied to the next batch, as well as new capabilities that we're completed during that early batch. Then, they do this for a few cycles until the last low rate production batch has very few issues. Then, they issue the first full rate production batch and later take back the earlier frames and either rebuild them to the final standard, use them for testing, or buy them back and scrap them.
This addresses the days of building hundreds of deficient fighters that had to be replaced with later and later models until they were done right, often while killing trained pilots. So, while it lengthens the development cycle a lot, what you eventually get is USUALLY well ironed out.
It isn't so bad with small arms, light vehicles, etc, but gets to be quite expensive on tanks, fighters and literal combat ships, and is absolutely abominable on things like Ford class carriers where much of the first one has been torn up and rebuilt multiple times and now the second one is beginning to have the same issues.
In the end, I am confident that the F35B will be a solid fighter, exemplifying all that a 5th generation fighter should be. It will also be one of the earliest in mass production (the F22 arguably being the first, but not having all of the 5th gen features fully integrated at the time) and will therefore be shown to be lacking in some areas as it ages as compared to newer designs. What it will be is a ton more affordable in the long run than the F22, both to produce and to maintain. I kind of wish that they would take the F22, integrate all of the lessons learned from its production and usage, and from the F35 development, and produce a "B" model that is the ultimate evoluton of that design.