Listen, I like solo lane swain right now. I play it a good amount. Consider me a minority here if you want. I'm sick and tired of people like you who don't even play the champ in solo lane well whining about him. He's strong.
Even though people love to claim that solo lane Swain sucks and feels bad, ALL the data suggest that Swain is viable mid for every stat sight. And as a Swain solo lane player I find him fun even with his limits. People whine about the high mana cost and low range, but like, learn to play the champ? You have a weaker lane and you scale into this AP Bruiser Monster by the mid game consistently.
U.gg All ranks 12.1 Mid https://u.gg/lol/champions/swain/build?role=middle&patch=12_1&rank=overall
Lolaytics plat+ last 30 days https://lolalytics.com/lol/swain/build/?lane=middle&patch=30
Lolalytics last 30 days all ranks https://lolalytics.com/lol/swain/build/?lane=middle&tier=all&patch=30
When I see people cry about Solo lane swain, I think "Do you even play Swain solo lane? did you bother to learn it?"
His limits are high mana cost and low range. You need to play around them. I think the only way they could reasonably shift him into a more solo lane role is if he is a mid laner and they give back some sustain he used to have at the cost of the passive hook ability.