I currently run training in two quite different simulators. In the more primitive when windshear is selected it produces fluctuations of IAS about 20 knots, with sink rate about 1000fpm. So this is a very crude simulation of just one type of windshear.
The more advanced simulator has preprogrammed models of generic and actual historical events, including increasing head and tailwinds on the runway and airborne. Several produce a rapid change of 25 knots in IAS, so I do think big and instantaneous changes would accompany a down burst over the runway, or occur in the surrounds of a dust devil. If the tail was already up it could be possible to ‘pin’ a taildragger to the runway and not go flying unintentionally, but if the tail was still down it would be airborne - like it or not - if the gust was strong enough. If the gust was sideways, even with the tail up the chances of a runway excursion would be high, no matter how skilled the pilot.
Sailing in the sub tropics, I once got too close to a water spout. Not much you can do to avoid them when you are doing 5 knots. I can assure you that the wind went from a few knots to about 40 in a trice. We got flattened, yet a minute or so later all was calm again. Scary stuff on water, potentially deadly in the air.