It's about BVR (beyond visual range) combat: launching a missile at a foe and killing him before he knows that you or the missile exist. It's also about survivability against enemy ground defenses attempting to lock onto you with radar and kill you with missiles.
For both of those things, stealth is a bare minimum requirement. The F-35 has it, the Eurofighter does not. (yes, stealth is not a binary property, but that is the TL;DR)
So the Typhoon is going to kick serious ass in certain situations and be completely unusable in others.