I always top the charts with arcane in any M+ all I do is spam AE and arcane orb with Arcane barrage.
Boss fights you just active all buffs and spam arcane blast. I sit around 10kdps and only 3k with fire.
For me fire seems extremely weak and clunky.
I like arcane, it has various playstyles, you can use any of the cov and do well. Its nice to have a spec that does not need a ground targeting spell, like flamestrike and Blizzard.
Fire is very powerful due to the controlled burst and utility, but that burst is difficult to execute well when pugging M+. If arcane gets a stun or more utility, it could gain some favor.
This is not a case of fire being weak. It’s you either not being optimized properly for fire or you don’t know how to play it well… or both. Arcane isn’t awful by any means, but it doesn’t compare to fire at its best.
This just means that you know how to handle arcane a whole lot more than the other, which is nice to stick to your strengths.