Why would it make more sense? Because you say so? Sereitei is already that. Soul Society is the planet and/or dimension. That dimension being the same size as the WOTL dimension which is based on our Earth and universe.I think the biggest issue about scaling is I seen some people literally treat Soul Society as a planet and not a City/State Capital. It would make much more sense for scaling. And if there are other planets in Hueco Mundo and SS if they are really saying they are their own universe.
These are all facts, this isn't a matter of opinion.