Thoughts on Battleline units

Recently my local community is beginning a new Age of Sigmar slow-grow league and as such I started building lists for various armies that I was interested in playing, one such army was that of Dark Elves since I have a relatively large, unpainted army from when I used to play WFB. As I began planning a list I began to get frustrated with how limited the battleline options are in Age of Sigmar with previous core choices in Dark Elves being removed such as dark riders and witch elves. These choices regain their battleline status when you have allegiance for that faction but this doesn't really work in practice, for example if you make your army only assassins and dark riders you can take them as battle line but who would ever play an army like that? This also stands in my opinion for units like flagellants, white lions, dire wolves and the like that are in very small insular factions.

The change I propose, and I'm seeing what the reddit community's opinion is on this is; Should leaders in factions instead unlock their units as battle line?

For example, if you take a lord-celestant then you unlock judicators and liberators as battle line, or if you take a death hag you unlock witch elves as battle line. Of course this limits people who field armies of a bunch of different choices as they would either have to field multiple leaders to unlock the options or rely on what few choices line up with their leader choices. But in larger games it allows you more diversity of battleline options rather than just spamming 3-4 of the few that match your allegiance. That said I am still fully on board with allegiance specific traits and items since buffing people for relying on a limited unit choice is fair.

Tldr: leaders should unlock battleline options instead of allegiances somewhat like 40k allied detachments.