Why would you need magical stuff? It does great damage without it. A simulacrum of your party archer would work just fine. He would do quite a bit of damage. Gate in an Goristro, bind him with Planar Binding for six months. Let your Simulacrum and your Goristro tee off on whatever you're fighting.
You think 1500 gold is a lot of cash? You must not allow your players to sell extra magic or hand out much coin treasure. That amount of cash is not real hard to come by save at low levels.
If you're using custom monsters, that's you. If you're going to spend attacks on the ranged simulacrum, so be it. It's your DM way of screwing the wizard out of power. If he gets the combo going and keeps him out of danger, he'll be hammering for a lot of damage.
If you're archer is doing that much damage, you must be making your monster's AC quite low and handing out magic weapons like candy. An archer's hit roll shouldn't be that much different than the wizard's. That -5 penalty for custom made creatures should be making them take a step back from using Sharpshooter. That's the main feat that separates damage.
Yeah. Martials do more damage. It shouldn't be 500 to 160ish. That's just poor wizarding or a DM that focuses way too much on screwing the wizard. His AoE damage alone against weaker encounters should put him way up there on damage. The only time he should be too far behind is against a low AC Legendary Creature that allows the archer to use Sharpshooter. If your custom made creatures allow that, they're not very tough are they?
Tell me have you ever used or seen a high level 17+ Fighter (with Sharpshooter etc) in play along side a Wizard?
I'm getting the feeling you haven't.
No magic items, against monster manual monsters. They out damage every single character in the party, the Wizard really can't keep up.
A sorcerer has a better chance of keeping up, but I haven't seen a high level Sorcerer yet. A SorcLock can out damage the Fighter, but that's actually a character that is truly overpowered.