That's probably true. The attendance at Conference matches (England's 5th division) is slightly ahead of Serie C.
Wigan are certainly worlds away from being Man City. But they're no tin pot club. Their stadium is quite impressive for their status. They were in the Europa League in 2013-14 as FA Cup Winners the year before. Owned by a multi-millionaire, two or three internationals on the roster. I'm not sure if they're that much worse than, say, Benevento in Serie A. And they're only 20ish miles from Manchester, so if there's one game they will have been up for, it's City.
Having drawn Southampton in the 1/4 finals, it's not inconceivable that they make the semis at Wembley. Where they'll get 50% of the gate receipts from 80k supporters, plus broadcast monies etc. The FA Cup is a great competition that make such a difference to the lower division clubs. It's a shame that the CL has devalued the tournament in the eyes of the top PL clubs.