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Epoxy resin would be better. You could try to just get back to the core and add a new wooden surround using epoxy resin. That would be a good combination of durability vs price.
Alternatively cut the bottom off and replace with a solid piece of pine, or some pieced together. Joined with dowels and epoxy.
Repaircare is a good epoxy to look at. They have a lot of examples on their site.
Airhead-
I'd thought about chopping out the bottom and replacing, but it's a substantial tiled roof so would need some kind of acro-prop arrangement at least or else it would come crashing down. If I didn't think it would collapse due to my crack handedness, that might actually Be the easiest option. It will be painted anyway so whatever solution it is doesn't need to be "wood"
stevo_com
Attentions now turn to the porch. The worst parts are the bases of the two uprights, which the previous owner ignored by sticking some mitred skirting around them. The porch as a whole feels solid, there's no movement, so I'm sure there's a core of decent wood in there. Question is what to do? Remove loose bits, wood hardener then build out with filler, sand and paint?