It´s not compatible with endgame combat:

Failed to load mods: EndgameCombat/data-updates.lua:7:EndgameCombat/prototypes/rangeturrets.lua:110: Tech set to boost turret 'artillery-wagon', which does not exist?!

Mods to be disabled:
EndgameCombat

So the damage increase to artillery wagons is valid tech and works as expected.

This is endgame combat throwing an error on purpose because they believe I'm doing something they don't consider valid.

Two options, either Reika removes the error check or I have to remove the tech when I detect Endgame Combat.

I would say contact Reika

comment out line 121 of rangeturrets.lua.

if all assignment attempts to base fail (in function on line 103), then line 122 will not run, which means the check on 121 is irrelevant. "if not base" does not need to be errored because the next line is "if base then",such that, nothing occurs if an attempt to change would cause a legit error.
But it also looks like that alone isn't enough, other errors in endgame combat get thrown after fixing this. damn.

after fixing this, endgame combat continues to throw error: "....__prototopyes/overrides.lua:142: attempt to perform arithmetic on global 'f' (a nil value).
he assigns f = 2 on line 92 of constants.lua with: local f = 2 --not needed to be big anymore, since have techs
in order for something to be considered a global and accessed outside it's own file, it cannot be set as local. so fixing this requires removing "local".

Endgame combat tries to do a lot of ambitious things. It doesn't just break with this mod unfortunately. It was breaking in my game before I discovered this mod. Every time a power pylon got destroyed in my game it would crash because of Endgame combat.

in that case, EC needs to add config options to opt out of those methods/functions. it's quite simple to implement just ...needs a bit of redesign.

I agree. I quite liked the EC mod. But I'm happy without it :D