40% is kind of an average of already installed offshore wind project, some having been installed 10 years ago... In wind project in general we've seen a continuous trend of spectacular increase in capacity factor [1], and 40% capacity factor can be expected from a US onshore wind project now... 60% average seems high right now (not in the future) and depend on geographies though

Of course managing intermittence is not easy and free, but nobody is talking about a 100% wind-power grid, and the current installations can absorb a fair amount of intermittence with extra investment... And wind and solar are becoming so cheap that you have a lot of space to pay for managing intermittence - that can be using differently the current installations, developing a demand-response market, and doing some thermal and electrical storage...

[1] see for example https://www.eia.gov/electricity/monthly/epm_table_grapher.ph... keeping in mind the average capacity factor include older equipment with low capacity factor... and that offshore wind is "just starting"