Arcteryx gear looks great and certainly did have a reputation for unrivalled quality when it was made in Canada.
But:
As Ben said, the Alpha is a lightweight jacket and, however well made it is, the materials aren't that durable.
I don't think Atcteryx has any clear edge over other top end brands when it comes to quality any more -- they're all made in China, no doubt with very strict quality controls, but even so...
The designs tend to follow North American requirements and sahions, not British or European ones. The hoods, in particular, are often not brilliant, having floppy or laminated brims that are fine with a helmet or even a baseball cap, but not on their own in driving sleet. Have a careful look at this before buying.
If cash is an issue, I reckon there are others that'll do the job at least as well for less.
Re the Changabang, do you really need pit zips? They seem like a great idea, but I hardly ever used them on a jacket I had which was fitted with them -- just too fiddly -- and they are a weakness. If great breathabiliy is essential, what about eVent?