I don’t think they were saying you shouldn’t ever look at the tacho, but that you should learn to be able to pick your shift points without having to look at the tacho.
As you say you do want to figure out what revs works best for a particular vehicle (having driven/ridden vehicles with redlines between 2500 and 19000rpm there I can say there is a little bit of variability to be found out there) but it shouldn’t take long to figure out what this sounds and feels like for regular use.
I don’t think they were saying you shouldn’t ever look at the tacho, but that you should learn to be able to pick your shift points without having to look at the tacho.
As you say you do want to figure out what revs works best for a particular vehicle (having driven/ridden vehicles with redlines between 2500 and 19000rpm there I can say there is a little bit of variability to be found out there) but it shouldn’t take long to figure out what this sounds and feels like for regular use.