Given the wealth of options to take for Elites/doctrine loadout, I can sympathize the feeling of being pigeon-holed into a certain playstyle (i.e. - you take Loota doctrines, so you should use lootas, right?). While I disagree with the premise that one must always build units according to their loadout buffs in order to do well (fundamentally, the game rewards adaptation more), it's clear that you should in some regard.
Why not expand the number of available Elites + Doctrines? Say, increase them from 3 to 4.
- You can now take 4 Elites and 4 army doctrines
This change will give a bit more player agency (customizing their army and all...) in giving them flexibility in "what to bring." while still retaining the fundamental loadout design.
Considering the # of Elites/doctrines (and the clear indication that more Elites/doctrines are to be made), it seems almost a waste to constrict the choice to just 3 of each (part of the sentiment of loadout limiting in-game choices). I think this simple change can make the difference between feeling constricted and feeling like you are filling out your army. Between the feeling of using a couple gimicky Elites/doctrines and feeling like you are taking your own custom army to battle.
An extra loadout slot will obviously also improve the strategic diversity of the game.