Seems more like an issue with being on a dead server than retail being a solo game. Low pop classic are the same as low pop retail, they arent exactly fun to be on, which is why many in the retail crowd wanted more sever connections.
I played on a medium pop server before moving to zuljin a high pop server… sure there is sharding and stuff but its a worlds of difference. Sounds like thats what happening with Earthfury.