I think you are near alone because it is bad advice. As referees there are many things that we want to be able to see, and we are always prioritizing. If you use the same priorities on how you think with qualified ARs as you do without ARs, then you are neglecting things that you should be able to focus on because you have the assistance of the ARs. That doesn't mean you have no responsibility for the things the AR helps with, but you should be less focused on those things than you would without ARs. And among the things you should be less focused on is offside position. (The R is much more able to help on actual involvement.) Especially at the professional level, it is completely reasonable for the R to accept that the AR will always have the best view of offside position and to spend his attention on other things. This is the extremely rare play that the R might have been able to help out on the position aspect of OS.
For those of us with less qualified ARs, we have to, IMO, assess the skill set of our ARs and use that to select our positioning and where we focus attention. I often have ARs with significantly different skill sets--that means I'm positioning different at one end and focusing differently at that end as well to be more focused on the calls the other AR is better able to help me with.
While I agree with the second half of your post, I really don't understand your first statement. The AR does have to determine if there was an offside offense committed--flag shouldn't go up until the player in OSP becomes actively involved, which is (in some cases) a judgment. I think I'm missing what you are trying to say.
you are welcome to deem my advice as a lot of things, but, bad, is insulting sorry. What works for some, might not work for all. Am not saying we as ref become the AR and are ready to call every offside etc. But, we need to be aware of what's going on and, the well used phrase, no surprises, comes into play.
Many a time the ref, at the very very, highest level has been shafted by an AR, who, for whatever reason, does not flag yet there is the ref, aware its offside, knowing its offside, but hey, how can it be offside as Mr ran the UEFA line for 10 years has not flagged.
You might wish to take issue with my, or anybody else's advice. You might wish to disagree with it. All good
Please don't state my advice here is bad.
Am of a school of thought, along with ELITE FIFA refs I have worked with, that, the referee is as fully aware of offside situations as possible where and when possible. Bear that in mind when choosing your words please.
Very few folk will offer advice that an entire forum can bow too or become moist over. But, if just one person gets a KMI correct because they were more aware of their environment then prev would have, job done. We all look to improve. We all find that improvement via differing methods.