The best keyword difficulty tool?

I have been using Ahrefs to measure the keyword difficulty tool, but it seems like a little bit flawed. Keyword 1 was mark 3 difficulty, but all the competitors are coming from subpages of Authority sites, with 0 to less backlinks targeted directly to that subpage. Some people viewed this as Very Hard to rank for.

What is your opinion on that, and does anybody here knows what's the best/accurate keyword difficulty tool?