Nothing strange at all about MWh/year. A MWh is just 1000 kWh, which is a very standard unit of energy.

With wind farms it makes more sense to talk about it's production in MWh rather than it's capacity in MW. The actual energy produced by a 253 MW array will vary significantly based on where it is sited, etc.

hours/year (= 1/8765.76) is a strange factor by which to multiply a perfectly good SI unit (MW).

Objectively it is strange, but it is the norm in that industry.

The watt (and hence kW and MW) are measurements of power, not energy. kWh (and MWh) are common, internationally accepted units for measuring energy.

Wind (and solar) energy production tends to vary seasonally, so it makes sense to use a year rather than some other time unit when discussing how much energy these things can produce.