It's more like if you make a plane resilient to bird strikes, you sacrifice a good chunk of performance - envelope, maneuverability, something.

Depending on how fast the plane is going, "good chunk" might be a hilarious understatement too. Hitting an object at 1000mph imparts 4x the damage compared to hitting an object at 500mph.

If you want to see an example of a durable military aircraft, look at the A-10:

(Hit by a literal bird, still flying: https://www.nbcrightnow.com/news/a-10-warthog-hits-bird-at-r...)

(Hit by idk what, giant hole in engine, engine on fire, still flying for an hour back to base: https://theaviationgeekclub.com/heres-another-story-10-warth...)

Anyways, that's a military plane designed to get hit by... stuff... and as a result can take bird strikes. But its max speed is like 400mph and it would get absolutely wrecked by any serious opposition from fighters. The more resilient you make a plane to birds, the more vulnerable it is to missiles, per unit price. And missiles is kinda the point of the whole endeavor.