The reason Seraphine mid has no popularity is because there is simply no reason to play it over apc, because apc is simply more broken. Matchups for bot lane are much better and you have an ally to power you up. If sera apc had similar win rates to mid, sera mid would've been picked more and I can guarantee you this. So I think its important to keep mid lane in mind when balancing apc.
At launch Seraphine only had play rate in mid and support. And it was overwhelmingly support even though support sucked and mid was OP.
Then the power levels got closer together. Mid Seraphine disappeared and support Seraphine is now 16x the pick rate on the same power level.
Then high MMR players discovered that Seraphine Bot is OP. So now she has some pick rate there in high MMR.
That's the entire history. Claiming anything else is straight up gaslighting.