You are so far agreeing with the points made in my paper? Again you say there are things you don’t agree with in the AIAG method, but yet you trust it?
There are many people who don’t understand the flaws of the AIAG method - they just blindly apply the rules, treating Guage R&R like a check box and then get confused when they don't ‘Pass’. There is a better way and a better use of MSA for understanding your measurement system and improving it so it that it helps you and it doesn’t hinder you. It is not and should not be treated like a just another black box requirement hurdle that needs to be jumped.
People should always be cautioned against using a black box, as in "garbage in, garbage out." I have seen this with non-normal data being put into a computer and a process performance index coming out the other end (based on the assumption of normality) which can underestimate the non-normal fraction by orders of magnitude.
Same for MSA--one has to follow the process for randomization of the parts, and also checking the results with the control chart of ranges to identify outliers that can, as you pointed out, contaminate the results.
If on the other hand we really use 10 parts and have two or three inspectors measure them, with randomization to exclude extraneous variation sources, and also consistent environmental conditions (where required, e.g. if temperature affects part dimensions), then the AIAG procedure, which also appears in textbooks and (as I recall) an ASTM standard, will deliver a reasonably good estimate of the equipment variation and appraiser variation. An alternative to the average and range method is to use two-way Analysis of Variance in which we know the F test will show the parts to be different (we expect them to be different due to part variation) and we hope the null hypothesis that the appraisers are identical will not be rejected. The variance components also can be isolated.
Even given the issue of the appraiser as fixed rather than random variation, detection of appraiser variation means this is an issue that can hopefully be addressed as shown in your example with the supplier appraisers versus the internal appraiser who used a different, and superior, method.