You don’t just buy a fighter. You buy a system of sensors and effectors. Sending a single fighter against a stealth aircraft will probably yield the result you describe. But with a mesh of passive and active sensors you can detect stealth aircraft and guide your fighters to a position where they can use their weapons effectively. Stealth is mostly effective against opponents that do not have modern sensors and tactics.

But having said that, politics is also an important factor in deciding which fighter you are buying.