Alpinestars are generally a very high quality make, their kit sells like hot cakes all round the world. Working at the UK distributor in the returns dept., I see very few A* items come back due to leaking/not waterproof. If you have a failure on a particular brand once, I would suggest that is not a good reason to then avoid that make like the plague. If you constantly have problems, or hear of other people having problems with a particular brand (and remember there are a lot of bull*****rs out there), then you may have reason to avoid that brand. Also bear in mind that like many things these days, you will probably avoid one make only to buy another that is actually made in the same country, with the same materials, and to the same standards - quite possibly even in the same factory!
I have also worked in several different bike shops, each time selling different brands, and I don't remember any particular brand being returned in large quantities over any other. Yes, occasionally a manufacturer introduces a model that hasn't been well designed/put together, but on the whole this is rare. I have mentioned elsewhere that I don't really like Spada boots. This is because Spada were at the time quite new to this area of clothing (talking about 2008 here), and had entered the market at the budget end. However, I have no doubt that if they stick with this line, they will improve given time, may even be a whole lot better by now - I just haven't seen any since then. They used to do a cracking pair of winter gloves back then, couldn't get enough of them in the shop. And much cheaper than any of the premium brands.
So, having said all of that, why exactly don't you trust A* gear to be waterproof? Have you had many bad experiences to this effect?