I'm in one of two minds, but neither involve the removal of positionals.

My first opinion is that the bad habit of bosses that change direction almost at random needs to be stamped out, as it completely disregards the tank's role in positioning the boss to make positionals easier for the melee players to hit them. Having more positionals wouldn't be a problem if the bosses actually stood still and didn't spin around randomly.

My second opinion is that positionals in high-end content limit the design space devs have for boss arenas, and that high-end content should either be designed with the explicit intention of positionals in mind (so no spinny teleporting nonsense), or should be omnipositional, so that the whole arena can be used for mechanics (See P2S as an example).