As a relatively new MFN-player, I would absolutely not have started playing the game, if my first experience had been in an older league taking over a dumpsterfire, playing against owners who had time to build their teams for a longer period of time.
In other sports games with promotion and relegation, it works because the bad teams go down and good teams go up, to even the playing field for everyone. In the MFN format, it just doesn't and because the AI is really bad with cap compared to what we can do as owners, taking over a team the AI has touched is often a really bad experience.
I'm more open to rebuilds now, but for a start, I think the entire experience of starting fresh and making all your own mistakes is an important learning experience.
tjynne, owner of Carolina in AGS (only league I play), took over from a bad first season and some time with AI controlling, so he has a worse team than I do and a cap that's in a worse condition. He's taking it in stride and his team is not terrible, but it's just a huge difference only 1½ season in.
I think the job is rather, that older leagues have to keep filling spots in their league as they become vacant. If you accept people leave and do nothing about it, you're setting yourself up for less owners in the long run.