You say hold, that means that if you are not around 12 P.M. you can still be Top10 even if people attack you? I think there is not one person who can sustain Top10 who doesn't spend a big load of money, thus having CS heroes.
If you refer that you are online near 12, and you can easily take a Top10 rank, that I do believe, it is not hard to do. There are Vip0 players in my server who are Top10 at closure time in a sea of CS heroes, then get dropped low.
I can hold Top10 but I have those heroes (at least Sylphi/Goram), biggest whale can hold Top1 even if he doesn't appear for days.
You definitely don't need CS heroes to hold top 10. In fact only just a few of the most recent CS heroes were good enough to use at 3* (sylphi/goram) in arena. All other heroes before that were not competitive against old 7* heroes.
Contrary to "popular belief", you need to spend very little to be able to be #1. You need a minimum amount of diamonds to reset 6x a day while levelling to up, and that's pretty much about it.