It’s a very good route through the Purbecks, but from the Grange arch, the route takes a zig zag road descent, along the road for a bit then into a mild descent with some boggy bits to Nordon farm, it’s got a shop and a couple of Peacocks, It’s a route I used regularly in the opposite direction, to get up on the ridge.
But instead you could add some great views, and a very good descent. Coming to Corfe from the Grange arch, when you get to the road here
https://maps.app.goo.gl/LZ55YAGyWUwnXfmK7?g_st=com.google.maps.preview.copy
Instead cross the road and stay on the ridge, up the short climb and you get a great view from the trig point at the top you enter a field as you leave, instead of following the main trail down to the right, head left at 45 degree heading up to the spine of the ridge, you will get to the highest spot as the woods end and a fence starts, (hop over the fence here, otherwise you have 3 gates to get through) )follow the fence line along the ridge then when you get to the small but fully opening gate go through it, stay on the highest bit and you get to the point, then head downhill and left to ride the chalky single track down to the Castle, there’s a footpath to Corfe which you can push/scoot along if there are people about, or nip along the road into Corfe village, Fox inn is the best pub for views if you sit at the end of the garden, and the village Bakery is excellent.
The segment from the view point to Corfe https://strava.app.link/DPFjGVRh6Jb
The route from the Grange arch to Corfe viewpoint
https://www.plotaroute.com/route/2640318?units=km