This is false. I've encountered the type you've mentioned, certainly, but I've also encountered those who hide behind it, and those who run around it to avoid fire. Even better, I've encountered those engie pairs, one healing and one wrangling. They're still easy to kill if you know how to deal with it. I've also met smart ones who know when to wrangle and when not to, and they do indeed tend to be more difficult, but not insurmountable.
My experience is also not limited to mesa. I have played and still play on basically every map we run with the exception of 2fort. I've not only used the wrangler extensively, but I've killed them too. I'd say my experience with them is just about as extensive as it could be with not even a week being past.
I'm not saying these things to blow my own horn; I'm saying them to tell you that I've got a variety of experience, and from what I've seen, they're easy in basically every circumstance, assuming you treat it as a big threat, and you plan on how to deal with it.
I stand by my statements that I do believe it'll fade into the 'rarely used weapon section' along with the DH, though. like I said, the only reason we're seeing so much use is because it's 'shiny' at the moment, and everyone wants a taste of it. That will go away soon, and I bet you that while a number of engies might carry it around, not many will actually use it that often.
I am not sure you understand the effectiveness of the battlement sg on 2fort map, especially one on the right in the screen shot. I am not familiar with mesa, but the 2fort battlement sg offers very unique advantages which is not available to another maps I play such as Dustbowl/Egypt and Gravel pit. Assuming the wrangler engi and another engi is competent, then only threat to them is a good sniper.
I do agree many people will stop using wrangler once shines wear off. So far I found wrangler to be very situational.