I find it awkward that you don't gain any new techniques as you tier up and progress. The same five you have at the start is the same five you'll have at even tier 6.
I suggest that every time you rank up you gain one of every previous technique tier, and be allowed to purchase up to double the starting amount of techniques.
So if you hit tier 6 you'd have 10 tier 1 techniques. 5, then 5 again. Then you'd be able to purchase up to five more which you'd also have to train for if not more than 3 tiers below your current tier.
If that seems like a lot, which it only kind of is, that's just a -maximum-, and you could always repeat the same techniques in multiple slots to further "master" it, allowing multiple uses despite cooldowns since they're separate technique slots with separate cooldowns.
I suggest that every time you rank up you gain one of every previous technique tier, and be allowed to purchase up to double the starting amount of techniques.
So if you hit tier 6 you'd have 10 tier 1 techniques. 5, then 5 again. Then you'd be able to purchase up to five more which you'd also have to train for if not more than 3 tiers below your current tier.
If that seems like a lot, which it only kind of is, that's just a -maximum-, and you could always repeat the same techniques in multiple slots to further "master" it, allowing multiple uses despite cooldowns since they're separate technique slots with separate cooldowns.