I don't find discoloration bad either, stains – well, they probably can't be avoided. Only if the wood crumbles immediately, that would be annoying. So it should last at least 10 years, I hope. I would also paint or oil it every year.
In that case, I stick to my recommendation. It should be available from Europe as well.
As far as I know, only various tropical woods are better in weather resistance, and those are not an option.
Robinia should last longer than 10 years, but it also costs quite a bit more than larch. If you can/would renew after 10 years, the tip with larch is still not bad. Disposing of wood is not trash in the usual sense, but rather a cradle-to-cradle thing.