My opinions based on thousands of hours of roaming. Again these are opinions for discussion and I am not saying these are all equal in their nastiness.
Condi Mirage - Why it is broken: Way too many condition types on one build with heavy condition spike wrapped in one of the most defensively minded offenses in the game. Tons of armor, solid hp, reflect, blocks, invisibility, teleports, invulnerability, etc. How to fix: Reduce the available condi types, outright limit the number of defensive options in one build and straight up remove reflect on dodge.
Power Rifle Deadeye - Why it is broken: It hits like a truck out of stealth and vanishes a second later. Condi doesn't stick to it and there aren't nearly enough reveals. The reveals that do exist are clunky or short range. How to fix: Stealth needs an exhaustion mechanic and Death's Retreat should not power up Lead Attacks.
Malicious Backstab Deadeye - Why it is broken: It hits like two trucks out of stealth and vanishes a second later. How to fix: Same as Power Rifle Deadeye.
Bonus! Underwater Ranger: Why it is broken: Virtually impossible to take down underwater which gives it a massive terrain advantage particularly around EBG Red Keep where packs often tie up the WP there and simply jump off into the water when challenged. How to fix: Downed while underwater needs to be removed, damage needs to be taken from falling when hitting water from high up and that pet heal needs a massive reduction.