I am confused what you are suggesting.
Yes, your baby titan score would start out lower than your adult titan score, but you would still be getting your 10* titan loot while you were leveling up your baby titan team. Just like you can fight in the Advanced challenge event scoreboard even without running a team in the Beginners or Intermediate challenge event scoreboard.
Besides 3* heroes are a terrible way of leveling heroes, 1* heroes are the best way to level (see note).
The advantage with alternating Adult titans with Baby titans is making alliances more inclusive. My alliance member are hitting 100k per Adult titan but I am happy if I get a cascade for 5k. If you just care about the end game player, you are going to have trouble retaining a player base. As more and more of your player base shifts to end game player, it walls out the new player.
Note 1)