I don’t think there’s any big secret to getting 10* heroes without resorting to the champagne and caviar pay-to-win lifestyle. IMO, there’s only one way to do it: PvP and lots of it. Farm those PvP gems, use them to bring one PvP store hero up to 10* as quick as you can (or do what I did and focus on only buying frags for one hero of each element). Literally don’t spend PvP gems on anything else. If you can suck it up, dump any other frags you get from events into those heroes as well. Once they are 10*, you only spend your PvP gems on buying heronium and that becomes your evolve fuel for all the other heroes that you really like.
I’ve been playing a little over 200 days and I’m VIP 5, so around $22 spent. Sitting on six 10* and three 9* heroes. It’s basically because I leveled up Matador, Gammond, and Drake to 10* as quickly as I could from the PvP store and now I just buy heronium with those frags. Sorta lucky that those are three heroes that have also never been removed from the PvP store.