Roger's articles are not about liking or not liking something, they are based on measurement, research and hands-on experience, and are immensely informative. But I wouldn't be concerned with that lens. This is what he wrote about the 100-400L II after pulling it apart and putting it back together again:
"I know I can’t really, without showing you dozens of other lenses, do a good job of impressing you with just how robustly engineered this lens is. I will say that the insides look more like what we’d expect to see in a 500mm f/4 or 600mm f/4 lens, rather than a telezoom. It’s by far the most heavily engineered zoom lens Aaron and I have ever seen; and we’ve seen the insides of dozens of lenses in this range.
Well done, Canon engineers, well done!"
Then, after doing some MTF and variance testing he wrote:
"Both the MTF and Consistency scores are just outstanding. The 100-400 has some of the highest consistency scores of any zoom lens we’ve ever tested. It waxes the Canon 70-200 f/2.8 IS II lens, for example, having far less copy-to-copy variation."
I just wish I could afford one!