That page shows the wrong thing, technically. The difference is most visible in taxa which don’t have many identifiers, so there isn’t much wrong with the list of Formicidae identifiers, but it’s misleading in some cases.
The proposal is to have a drop-down list on the observation page, which would reduce your process to one step. I think that would have no effect on the number of people who tag identifiers immediately after posting an observation. It would, however, make it more likely they’d each tag different local identifiers instead of the current situation where many of them tag the same identifier who is at the top of a global list for some taxon. Making it easier for people to tag different local identifiers is pretty much the whole point of this feature request.
People who rapidly tag the same person on multiple observations are a whole different issue I think. Often it seems to happen when they notice someone identified a couple of their observations, and proceed to tag that person on all their observations in the same general taxon. Pointing out that a single request to review their other observations would have done the trick is usually enough to make them realize there’s a way which requires less effort on their part.
That’s a good point. Filtering out identifiers who haven’t logged in for a long while would be useful for people tagging identifiers, even though not improving the iNaturalist experience for top identifiers the way filtering by location would.