u/rp4888

This is the fix I would do personally if i could do an errata of features. Just one paragraph.

Add to favored enemy

"Additionally, When you fail a saving throw to maintain concentration on a spell, you can expend 1 use of favored enemy and choose to succeed instead. Once you use this feature, damage cannot break your concentration until the end of the current turn"

Yes that's really it.

To those interested, For a revamp that doesn't errata the 5.5 PHB. I previously made a post on how I would fix ranger via spells, I liked that route because it requires no errata or changes to the core book. That can be viewed here. https://www.reddit.com/r/DnD5CommunityRanger/comments/1skkh90/more_marks/