Look at almost every team that made it to 2nd division, and you will see it is the same time they struggled to produce talents to 1st team, be it Seville, Bilbao, Barca, Villarreal or even RM to some lesser extent.
All teams are developing talents at much better rate when they are in 3rd division or even 4th division, we struggled to develop talent badly during the 5 years spain in 2nd division even with the perfect mix veterans and La Masia kid.
Theoretically it seems good to put team in 2nd division, but by now there is enough evidence to prove otherwise in reality.
I'm not sure though that being in Segunda is worse for developing players. I think we relegated because we didn't have the necessary talents nor the signings. Of course there is a question of sustainability if we only rely on La Masia players.
I would argue if we get the balance right, that there is leverage in our advantage in being in the second division compared to the B division. That leverage would be scouring the second divisions of Spain, France, Portugal for the next Ndombele's, Pepe's, etc before they move to Ligue 1 side's, and also not facing the bureaucratic issues with Roland and Gabriel, and lastly avoiding the bureaucratic issue with Wague while also being able to sign as many african players as we like.
That is where I see the potential in being in the Second division, where our budget compared to what Villarreal and Sevilla can spend on their B teams can be to our advantage.
The counter point is that we would limit La Masia players in the B team bar the very best, which may cause some players to look for greener pastures.