If you’re following the 6-8 encounter, 2-3 short rest adventure day guidelines, the Arcane archer should be getting about one Arcane Shot per encounter. +2d6 damage with a minor bonus effect once per fight is pretty good for a Fighter Subclass. It’s got much higher average damage output than the Battlemaster with +1d8 every other encounter, though the Maneuvers have better rider effects. The subclass is theoretically well-balanced, the issue is that a lot of DMs don’t consistently follow the 6-8 encounter, 2-3 short rest guideline, which can cause Arcane Archers (and really any Class or Subclass that relies on short rest recovery) to fall behind its expected damage output. If this is the issue you are facing, I would recommend just giving them one use of Arcane Shot, and moving the Ever-Ready Shot feature to 3rd level, replacing it with a second use of Arcane Shot at 15th level. That will give you exactly the same damage output per encounter across 20 levels, but swapping the order will make that damage more consistent at early levels.
Another potential issue is that the Subclass’s design doesn’t mesh with a lot of players’ expectations of how something called an “Arcane Archer” should feel. A lot of players to whom the concept of the Arcane Archer appeals envision a character who’s got a magic arrow for every situation. But with only one Arcane Shot per encounter on average, that’s not how it plays out. Players want to be deciding “which Arcane Shot option should I use this turn?”, but the design wants you to be deciding “should I use my Arcane Shot this turn?” It really should have been called Arcane Sniper, because that’s what it’s designed to be; the character who has one extra-powerful shot that they have to plan carefully to make the most of. You can see this in the D&D Beyond interview with Mearls about it, he even mentions the sniper character from his game that the Arcane Archer was supposed to encapsulate. If this is the problem your player is having, I would recommend decreasing the damage of all Arcane Shot options by 1d6 (2d6 at 18th level) and giving them 4 uses instead of 2. You could even give them 4 more uses at 18th level instead of the damage increase if you like. That will give the same average damage output, but give the player more opportunities to use their Subclass’s defining feature.
