The thing is none of these generations of side-kicks will ever truly grow up to replace their mentors (at least not in a long term capacity) as the concept implies but writers will always want to introduce original young heroes as it a easy, relatable storyline new readers can identify and get invested in and there's a good chance their creation will go on to become a profitable, widely loved fan favourite with the current readership.
It does leave a lot of these teen heroes stuck in a sort of perpetual limbo, Tim Drake is a prime example as once Damian was introduced he became largely redundant and has been increasingly diminished and ignored ever since.
I guess all you can do is enjoy and support any workss they still appear in and hope your own faves can carve out a niche before then because I'd imagine a good number of these generational heroes will be forgotten entirely once the potential 6th generation starts appearing in about 10 years or so.