Just IMO:
In modern football, the personnel doesn't define the scheme, the personnel is just one way to execute the scheme.
Like 30 years ago, guys like Urban Meyer were running power football out of spread formations.
With respect to the 2025 Rams, 13 personnel was just one personnel package that the Rams used to execute the same plays that they ran from other personnel packages. Here's what one opposing DC said about it:
@10:52
View: https://youtu.be/c_38vZYOoxI?si=--L_mTpg6jzOdO5S&t=652
The DC ^ also noted that 13 isn't something that is seen a lot. The rarity undoubtedly contributed to the Rams success.
Underscoring the interchangeability of plays between personnel groupings, Sean has historically had the TEs learn the entire offense, not just one individual player's responsibilities. In his 2025 roundup, Sean complimented Ferg's ability to (basically) play all the other receiver positions in the offense.
From a roster standpont, 13 can take advantage of opponent rosters. You got teams who don't have enough guys who can matchup with 3 semi-capable "big" receivers on the field at once. You got teams playing their deep depth chart linebackers - many of which are just not that good.
Also, from a moneyball standpoint, with the rising cost of WRs, Tight Ends have become an increasingly cost-effective alternative.
13 personnel is a nice option to implementing the Rams offense. Defenses adapt and don't be surprised if there is a drop-off in offensive efficiency this year and/or next year.