The nuclear weapons in Germany are from the US, and the US refuses to help adapt them for fighter jets other than US made.

You need tiers of capability. Nukes are one, but a more readily used one is the ability to knock out (or at least suppress) ground based air defense. Stealth aircraft like the F-35 are perfect for this mission, they can get in range, fire off an anti-radiation missile, and get out. Non-stealth aircraft may be forced to turn back before they get their shot off, thus leaving the enemy air-defense active and forcing a scrub of the planned attack on what the air defense was defending.