Unless your archer has 1200' range or some long range teleports to back him up then he won't stand a chance to the 1200' far shooting tactics. He does 0 damage when not in range.
Originally, I had a rune Scribe multiclass that doubled the range of a ranged weapon so I did have 1200 feet range with longbow. It wasn't until I made that build that he added "No UA" to the list of restrictions for everyone except himself.
But even with that, since he seeks to have an ever increasing list of magic items, we can just grab the actual Rune itself from SKT that does the same thing.
Or we can wait until he's within 600 feet, since he insists on using spells that require close range while also insisting that he's at the maximum eldritch blast range possible. He's both at once. Like a proton jumping orbitals.
The original build was a champion 17/rune Scribe 3, using the vend rune to double range of the weapon, with an oath bow. 6d6 from oath bow, 2d8 from both itself, 24d6 from poison, plus 15 for sharpshooter and Dex.
Since then, he's moved the goalposts. He's added immunity to poison, he's added no UA, he's added level restrictions, he's added a ton of magic items to his own build, and more.
I had an updated version that removed the rune Scribe (no UA) and changed it to arcane thief. Added 6d6 sneak attack. Why all the large dice numbers? Because this build was based on critical hit probabilities only, using the standard DPR equation that modifies damage based on the probability to hit. It ended up being around 30-50 damage per shot (depending on whether I had advantage, the likelihood of his losing concentration, and more). But it was still enough to kill him with his 200+ HP and his Sim with around 75 HP in two rounds.
I'll note that he doesn't have 200+ HP anymore. He's no longer using armor of agathys and a 7th level Aid spell to give him an HP boost. So his 145 HP is much easier to take out.
For example, with my pyromancer build and a single meteor swarm spell, dealing an average of ~150 damage per meteor (damage increase is due to elemental adept and flames of Phlegethon feats). He's since changed up his magic items to make him have advantage against spells, so it may be a bit lower now. I haven't done the math yet.