For civilizations that do not have access to the arsenal, in case of allying with minor facsions it would be good that in those places exclusively for facsions without arsenal, there are 3 improvements available:
In case of being gunpowder cavalry, add the upgrade ‘cavalry snail’
In case they are skirmishers add ‘anti-infantry rifles’
In case they are musketeers add ‘socket bayonet’
This would make native allies more useful for civilizations that lack these technologies. For example, when the Aztecs take the alliance with the Jesuits and cannot improve the reach of the conquerors because they do not have arsenal. This would be more useful to the natives for civilizations without gunpowder and at the same time it would give more balance in the game and usefulness to the natives.
Another example would be an alliance of Aztecs with the Cree where they have access of anti-infantry rifles:
This will greatly improve the natives for civilizations without access to the arsenal. It would even seem fair to me that the upgrades ‘flintlock rifle’ and ‘paper cartridges’ were also available in these native villages. (If the ally is a skirmisher or musketeer, of course)