I'd rather err on the side of abundance, than come up short in an all out war
Yes, EB is making very capable submarines, but the fact is they are now running $2 billion per sub. We do not have infinite monetary resources. It would be nice to have as many as possible, but the facts are there is a procurement cost and the then continued cost of manning and upkeep. So it is a balancing act for the total military budget. And, the F-35 (our other topic) is really eating up the defense budget, putting pressure on other programs. That said, the Virginias are being delivered below cost and ahead of schedule, and EB is considered the poster child for doing things right in meeting or exceeding program goals.
In case you want a comparison, the Los Angeles class was around $180-200 million per sub. Hence you could buy 10 LAs for the cost of one Virginia class sub in the 1980's.
What the hell is Armageton? There is Armageddon from the Book of Revelations (also Armageddon starring Bruce Willis). But no Armageton...
If we do have your actual "Final Battle", it would probably include nuclear weapons. In which case it will be over in 2-3 days.