No offense taken, and I hope it's mutual. I respect your experience and opinions, and look forward to different points of view in these threads.
My 'main' way of sharpening is to take several chains per saw, swap them out in the field, and sharpen them back home on a 511 type grinder. Same grinder I use when I have a bunch of other people's loops to sharpen - it's just faster, and I get consistent angles, cutter lengths, etc. Sometimes, I 'touch up' with a file in the field, but it takes a bit of forethought/understanding of subtle differences to be able to go back and forth between methods / tools.
I have enjoyed 'playing'/experimenting with a variety of grinders, file guides, rotary tools, etc. to sharpen chains, and believe that almost any of the more common ones can be used to make an acceptably cutting chain ***if the person using it understands how it works, and what they want the finished cutters to look like ***. I am convinced that people can also completely ruin, new-out-of-the-box loops with any of these tools or methods, if they have no idea of what they are doing! So, if someone has a method that works for them (any method), that is great - I don't care what it is (although, I might be interested, just out of curiosity).
I agree that there are a lot of guys who think that they are better at a lot of things than they objectively are - my earlier comments were meant to say that those who really are good with free-hand filing probably don't bring their chains in for someone else to sharpen. I have seen a lot of the 'other guys' chains - with random length cutters, and random angles. Often, with Left and Right cutters looking like they belong to different chains.
I have noted in some of these discussions a difference in the definition of 'sharpening' that has led to confusion. Some guys 'touch up' each cutter with one or two file passes each time they fill the tank with fuel - essentially 'maintaining a sharp edge'. Other guys wait until the front and back of the cutter look the same, then have to take off a lot of metal to restore it. Can't really compare these as 'the same thing'. I disagree with your comment "filing round ground chain is mostly a waste of time". I do not see this with touch up filing, which takes just a few minutes, or even with more extensive filing, using some type of file guide or jig (5 or 6 strokes?) to keep things accurate and consistent. For rocked chains, a full-sized grinder rules. If you work in the production environment you describe, swapping chains might be a better choice, although, I would still toss them into a box, and sharpen them on a rain day, pay someone to sharpen them, or put them on eBay or CL as 'once used chains' (which some people do).
I also have to disagree with the comment "low kick back . . . chain isn't really meant to be sharpened". The cutting speed may be objectively slower in some situations, but it is not practically noticeable for many users, where actual cutting comprises only a limited portion of their work time, once handling of the wood, etc. is figured in. Especially when cutting smaller diameter wood (16 - 18" diameter or less) where chip clearance is not an issue. The tie strap bumpers (OP's chain) are more obtrusive in this way than the drive link style bumpers, which have largely replaced them in most situations. I have sharpened both of these types down to end-of-life conditions, where they cut acceptably for me. I have also received and reconditioned a bunch of these chains after provoking people to send them to me, instead of throwing them out!
I like pictures too, although, it takes a pretty high quality photo to diagnose a chain over the Internet.
Philbert