It's interesting that the meta has taken this direction, and it's a sign of good unit/game balance. It's mentally easier to keep pumping resources into the factories that are already producing units, rather than focusing it on the superweapons, and it gives a payoff much sooner (while a superweapon costs much more, and gives you nothing until its finished).
I think that the other reason why team games (especially large team games) turn into arty spam contests is because people build a lot of static defenses, and artillery counters that hard.
However, if you want to beat arty spam, you do have some options, but they often require a bit more mental effort/practice. Generally, you want to have attacked earlier in the game and prevented the buildup of arty but... sometimes you just don't have a choice. Some options are:
-Construct Cornea/Iris units to cloak your raiders' movements, and use fast-moving strikes to hit and run before the arty shells arrive (note: you cannot cloak shielded units). Scythes and/or ultimatums are excellent alternatives, but you can always morph a cornea to an iris to attack with different raiders. A personal favorite tactic of mine is to make a handful of corneas in patches around the map, and fly Revenant gunships to surprise attack and then retreat back to safety quickly.
-Along those lines, use terraform to create radar blocks (often players forget to build additional radar to see around this). These terraformed objects can also soak artillery fire. Many people just build a wall, but it's probably more effective defensively to build a bunch of high pillars, making an enemy advance more difficult (so you kill them a few at a time if they attack), but maintaining it is much more difficult.
-Construct hardened turrets (Razor, Gauss, Faraday), which take reduced damage when not deployed and heal while closed. Set them to hold fire, and bury a caretaker nearby. The enemy will waste shells targeting your turret, and it'll remain at full health unless assaulted. Preferably, build these turrets up high, so assaulting them is even more difficult
-Speaking of burying caretakers, remember that burying things can help prevent detection. I've even seen [Rooks]Vegan bury stinger turrets to a perfect depths so they don't show up on radar/visually, but they can still fire over the ground level.
-Construct a few (not too many) cheap units to patrol ahead of your front line in order to soak fire from slower-firing artillery units (not ideal, because it costs you metal, but you can set fleas or hermits to patrol, and an enemy who isn't paying attention might not realize they're wasting shots).
-Build Arty of your own, and terraform a ramp to give you better range than the enemy.
-ATTACK! Sometimes, your enemy has seen you try to be tricky with aerial sneak attacks or raiders and prepared for those targets with the appropriate turrets. Switch it up and swing with a dozen cheap assault units, like hermits or Ravagers (which actually isn't that huge of a mass investment). Preferably, attack a corridor that you haven't focused on yet - hopefully their defenses aren't as strong there.
Of course, these tactics aren't easy, especially if you've been playing for a while and/or your're tired. Heck, my own rank is obviously not high enough to make a statement about how effective these are. But hey, give these a try.