Having the ability to select lower-cost options that are Good Enough In The Context might be worth the higher cost of maintaining two supply lines. Plus, not every mission is going to need the F-35. Having to shoehorn the F-35 into every possible mission seems wasteful, if we can have a plane that costs half as much for the lighter missions, or twice as many of the cheaper plane.

Yeah, I've seen this idea floated that we may go for a split fleet of about 40 F-35s and 80 Gripens (which I assume is what you're nodding at). To my mind this sounds like an excellent solution, both for the reasons you outlined above, and because it addresses both the Russian threat and our own need to be less dependent on the US, militarily and economically. It gives us a weapons platform that substantially overmatches anything in the Russian fleet, and a weapons platform that we can reliably fly and maintain in any hypothetical future conflict.

In regards to how the F-35 fares in a defensive context, there's a pernicious myth that stealth only matters for first strike. If that's what you're alluding to, the simple reality is that all warfare is about stealth. That's why our soldiers don't only wear camouflage when they're attacking. Seeing the enemy before they see you is the single biggest advantage you can possibly have in any form of warfare. That's true of infantry, tanks, ships, airplanes... It doesn't matter. Stealth wins fights, no matter the context, with very few exceptions.