One key difference. F-15 has to see and point at the F-35 to acquire a missile lock. On a stealth plane, this is no easy task. The F-35 can target multiple planes simultaneously without pointing at rhe aircraft, or even being in the area. A different F-35 can acquire the targets while the wingman targets and fires. That’s a trick no one else can match. What one aircraft sees, they all see.
They can do it with UCAVs too.
Which is, of course, the future of air combat.
Each manned aircraft controlling 2-6 UCAVs and operating as a single, integrated unit.
Throw in a little AI and you have magic.