" When Crypto’s Surveillance Drone detects and enemy near Crypto they’re marked for Crypto and his allies to see. "
What is wrong with this Passive ability? Well… it's not really a Passive. Think of all the other legend's Passives:
Bangalore: Faster when shot
Bloodhound: Sees tracks
Caustic: Immune to Nox Gas
Gibraltar: Gun Shield
Lifeline: Heals faster
Mirage: Invisible when knocked
Octane: Regenerates health
Pathfinder: Uses survey beacons
Wraith: Notified when people aim at her
Wattson: Accelerates fully regenerate Ult
What do all these have in common? They help the specific character in a general way. What this means is that each Passive ability on the list could "potentially" be a passive for someone else, but its not. Bloodhound's passive is specific in the sense that it only helps him, but its general in the sense that it could help others if they had it. Lifeline could see other people's tracks, but she doesn't because that's bloodhound's thing. This is what makes a Passive a Passive.
Crypto's passive is flawed because it doesn't abide by this rule. It is not a thing that helps Crypto in a way that is unique to him. It fails on both counts because it doesn't help him specifically, and no other characters could have the passive. This means that his Passive is not even a Passive by the developer's own standards. The ability to detect enemies out of the drone should simply be part of the drone's kit itself. It is something that comes from the drone and everybody benefits from, it misses the mark for a Passive ability by a mile. If Respawn simply made that ability part of the drone by default and gave Crypto a Passive such as "unaffected by drone EMP's" (similarly to Caustic's nox Passive), that would make his kit much more viable and have higher pick rates.
Disclaimer: I am a top 150 crypto player with 1200 kills and also main Crypto for Predator lobbies.