Why do people h8 brave lyn so much?

Here's one

Because there's always a chance that you'll run into them during the Arena and wreck your team (roughly an 80% chance).

Reinhardt's Dire Thunder: Destroys 100% of all Red Sword users

Brave Lyn's Sacae's Blessing: Negates all DC units barring dragons

Both have good atk and with Brave B.Lyn and Reinhardt and given Death Blow both can just out right destroy units with Cav emblem boosts, and with Sacea's Blessing B.Lyn can be even scarier

They’re annoying to deal with. Rein just loves to spam DB, Chill res or lancebreaker, moonbow, and QP and Lyn is just way too fast with Mulagir and they can kill many meta threats with their massive range. I make sure I always have a unit to counter them in arena.

I've found a team consisting of only brave Lyn in arena

1. Murgleis cancels magic buffs
2. Swift Sparrow
3. Sacae’s Blessing
4. Access to Firesweep Bow
5. Often paired with PA!Azura

There’s a lot to unpack here but let’s just throw away the whole suitcase

it's an annoying, easy to build, easy to score points duo so pple see them a lot and so complain about it...
I personally run my +Res MGrima with deflect magic for precisely them, can't die to Lyn and can retaliate, survives a fully buffed moonbow QP Reinhardt ( provided he's not +10 but i'm not high enough in arena (18.5) to meet those :p