I didn't say you weren't allowed to state your position or opinion. I'm telling you what my opinion of your suggestion is. You even asked people to do this in your original post. I suppose you only wanted/expected people to agree with you, but things don't always work out that way.

I think your suggestion is bad. No, you should not be able to level up more than one job at the same time. The only reason SMN/SCH can do this is because of the original planned design which they quickly realized doesn't work well in practice. It does not need to be tacked onto other jobs that have nothing whatsoever in common with each other.