The only thing all arms race games have is the whining, sadly.
Personally, I'm having a lot of fun in this game, even if other people get upset.
And even if they did get rifling... well, magic greek fire throwing ballista that hit with pinpoint accuracy from extreme range is just as unhistoric, isn't it? It's not like any arms race game is strictly realistic, and this is a magic one in the first place. From fireballs to directed lightning strikes to the weaponized terraforming that is the temperature manipulation... none of that showed up in history either. What does 'Realism' have to do with it? They do rifling, sure, sure. At least that's, you know, physically possible, unlike our telepathy, probability manipulation, weather control, divination, and complete immunity to the knock on effects of manpower loss.
I mean, if they replaced their cannons with lightning magic powered railguns, that'd still be just as unrealistic and non-historical as rifling but is still just as distinctly possible. Hell, that's literally what I was originally going to suggest after they made their cannons, I just got on late and by that time the magic ballista already had votes going for them and I didn't feel like arguing about it. Who gives a crap about history? A fricking wizard did it, for realz.
How much does it really matter, in the end, as long as we're all having fun making up new designs and killing each other?
It's not like it's unfairly balanced in effect. We've both spent around the same amount of turns on artillery, and hell, for all the complaining we can see around here about the enemy's advancements, I'd like to point out we're still winning the artillery duel.