Flamers are good in only some very few cases:
1. It's a tertiary weapon system for the model, meaning it can do its job without the flamers and the flamer is just a nice to have thing that doesn't take the slot of something better
2. It's a unit with tons of flamers so the amount of dice you throw at the opponent solves most problems (T'au Crisis units with 9+ flamer is a good example for that)
3. The unit has the FLY keyword so it can fall back and keep shooting and is durable enough to utilize it (or has a similar rule like Baneblades)
Now when we look at the Predator he doesn't check any of these boxes. They are his main weapons, but he has only three of them and he also doesn't have any rule that allows him to fall back and keep shooting. 3 Flamer, no matter how strong they are, doesn't help you against hordes much. Flamestorm cannons and Heavy flamer might help you against more elite infantry but a mob of 30 boyz or 40 cultists etc just laughs about the 9 models you just killed in overwatch. 18 If you were able to shoot at them the turn before which isn't always a given. And if the enemy charges your Predator with a transport or other non-shooty vehicle first to soak up the overwatch its even worse.
Edited by sfPanzer, 12 January 2019 - 07:10 AM.