[kvb]

Your particular example doesn't seem especially object oriented (e.g. it looks like a simple data type with a "smart constructor", which is a common pattern in, say, Haskell, too). But in any case F# supports both discriminated unions as well as normal OO design, while C# supports only the latter, so in that subset of cases that are better modeled by DUs F# will be strictly better, and in the rest of the cases it won't be worse.