otherwise everything is planned out between time periods that are the same as when it comes out a year later

How do you know that ? I don't think Atatsuki ever released their working schedule publicly...

And what would these types of events do to the game in the long run

About the Vegeta-LGE you mentioned, since it's actually hype content, they probably though of it long ago, and won't release it until enough time has elapsed since the LGE came out. They need to space out the content in order to be able to last in the long run.

Regarding the story events that other people were suggesting, it's even worse imo. The source material is limited, and they need to save those for future theme-based celebrations. In short, if they release content too quickly, they'll burn through the source material and will end up running out of ideas...