Do the above figures seem realistic?
Sounds about right. I tell passengers that there's about a 1 in 2 chance of cancellation in summer, and 2 in 3 chance of cancellation in winter.
I've been trying to be deliberately a little pessimistic. Your figures suggest nearer 1 in 3 in summer, 1 in 2 in winter.
Your weather filter seems reasonable (adding a requirement for 8km visibility would knock out a few more days). However some days the weather can be good enough for some purposes but not others, so you can still have a lesson on something, but maybe not on the exercises that were next on your list. For example you can do a dual navigation exercise when it may be too windy for you to do the landing (I've certainly done IMCr lessons on days when I couldn't land the aircraft); and you can do circuits on days when the cloud base is too low for cross-country flying.
When you've got a licence and are making your own decisions it gets more difficult. For example gusts are rarely as bad as forecast (although they are sometimes!), so in particular when there are forecast gusts straight down the runway it's quite often actually flyable ... sometimes I can't tell without going to the airport and chatting to people who have already been flying that day.