I'd wait to criticize the price/value of the new Sigma 135 Art until people are actually using the lens and indicating whether it's better or worse than the Canon or other competitors.
Fact is, there is no such thing as a 135mm lens available to consumers in f/1.8 until a few weeks from now. When that happens, different people will have different priorities, and we can differ on the perceived value of the lens. To pre-suppose that it'll be bad at something just reveals an initial likely bias; which is good because it can instruct you on where you might endeavor to be especially careful to be neutral in the event you actually get personal experience with the lens.
We all may do well also to be mindful that not only is the Art series quite a departure from Sigma's older line-up and build quality, but also that the latter entries in the Art series appear to have largely quashed some of the reported complaints, such as AF inconsistency and lack of weather sealing. This may or may not prove to be a consistent trend, but it needs to be taken into account if you are speculating based on earlier performance.
And, finally, the introduction of the dock does go a long way to enabling Art glass to exceed at times Canon L glass (speaking as one who uses both). And to prevent the lens from being bricked by new Canon firmware. If you go merely by internet reports of performance, then you are often being guided by people who do not have the dock or the patience to use the dock, or who use the dock incorrectly. You can very well argue that you shouldn't have to use the dock, and for many people that is absolutely right. In that case, using L glass is a great option - or if you don't even need that resolution and quality - kit glass. If it suits desired time spent / image quality ratio, these can be superior options, and no one should judge otherwise.
But my own hunch - which I was previously trying to suppress prior to the delivery of the 135mm Art - is that this one may have the opportunity to well exceed the quality of the eventual Canon 135 L replacement that is likely to cost $1800+, and quite possibly substantially more.
I look forward to the mid-April bursting forth of many reviews, positive and negative. It'll be fascinating, and in the very least, it will be pushing the other vendors perhaps not wait a decade or two to update their equivalents.