These comments surprise me, if only because the Tamron 24-70 VC offers exactly what you say people are looking for at a price that already seriously undercuts the Canon non IS version. I don't personally think that a new version is worth more than the original price point of the 24-70LII unless it offers something more than just IS, particularly if that comes at the cost of higher weight and slightly compromised optics.
Perhaps, although you could argue that the Tamron 24-70 VC had/has a QC/manufacturing issue significantly greater than anything in the 24-70 II:
Also I have read of some getting error codes with the Tamron. But, never a good thing when lens elements fall off.
Finally, the Tamron is lower IQ than the 24-70 II in the corners - whether Canon can improve on that is another question. The AF is also slower.
But the Tamron is an option.