Woof woof, mileages do vary, and I do take the time to consider my humble comments probably just as much as you do yours. In the end its just personal opinions based on observations.
Both my and my real (As opposed to Inter web type) friends experiences have been of some new model Sigmas braking and taking many, many months to be repaired while waiting for parts. Of repeat send backs till they finally get it repaired right with new models, and of mid-range lenses out of production for only a few (3,4,5) years not being able to be repaired "Because they don't make the parts any more". I and no body I know, has had a Canon lens break (YET), but "Reports" don't mention any none repairs due to lack of parts or experience with that model, do they? The longer a model is in production for without change, the more likely repairers will know how to fix them, and parts be in stock. Independent lens manufacturers make major model changes far more often than Canon, Nikon et-al.
Sigma have over the recent (5-10) years had many "Reported", compatibility problems with their lenses and some new cameras (All digital) particularly from Canon. Lenses which spring to my mind are 300mm f2.8, 80?-200mm f2.8, 80-400 OIS and some mid range, mid priced zooms. It may have only been one batch of each, it may have only been for the first few months of a new body's production, and they may have only needed "Re-chipping". And thats with out going back to film days. I've never heard of ANY Canon or Pentax or Nikon lenses having ANY compatibility issues with ANY of their respective body's have you?
Sigma may have improved a lot over the last five years, and yes some of the current lenses seem very interesting. But to ME, a company's past poor performance takes many many years (Decades even)to over come. And to ME, past performance IS some indication of future performance. And I know of no laws which force any company to provide parts and repairs for any length of time after production ends, is there any?
I MAY be tempted to buy a Sigma in the next few years, and I HAVE recently bought a Tamron for the lad, but that was cheep
second hand. Cheep enough to take a chance, if it cant be repaired in five years, theres not a lot to loose. But with a NEW, DECENT priced type lens, hmm different story. I expect to be using a top of the range lens many decades into the future, and if (When) it breaks, I expect to be able to get it repaired. Perhaps its because I'm old (Fashioned). Things built to a quality standard not an in built replacement time code. "A thing of beauty is a joy forever" and all that.
At the end of the day its, my experiences, my opinions, my money, my choice. Yours might be very different, and good that it is! If all our shots came out looking the same it wouldn't be a very interesting life would it?
Just MHO and my addition to the chat FWIW. Another evening gone forever! Time to go back to photography - TTFN