So if we look at these charts it would lead us to believe we would get a bit more reach with the 7D II. This sound very good. But this is a zoom lens, and that cripples the benefit, why buy a zoom lens to only shoot at the longest length like a prime? Any shot you can make under 400mm that can be properly framed will have a greater benefit in IQ with the FF than the gain you make in reach using the crop. This is just something to weigh out if a person is choosing a body to go with the lens.
I'd choose any modern FF camera, no matter how gimped, over a 7D or 7DII for wildlife.