Reverse-Cycle of Experience-Counter Commanders

I really like the Commander 2015 cycle of legendary creatures that grant you experience counters over the course of a game. Since only half of the color pairs were used, I wanted to take on the task of creating a cycle of legendary creatures in the opposite direction that still gain experience counters. I just want to know if I've made them massively overpowered or something.

It was important to me that I hit the following design points:

1. These new commanders should be ally-colored, not enemy-colored like the ones in Commander 2015.
2. These new commanders should have new ways of acquiring experience counters, and new kinds of benefits from doing so.
3. They should go together: the C15 commanders don't really interact with each other, but I think there's design space for two of these commanders to work in the same shard- or tribe-colored deck alongside each other. Hence, commanders that share a color will have effects that play off of each other.
4. Their power levels should mirror those of the C15 commanders, with very similar CMCs and P/T.

Also, I almost exclusively play Commander, so I'll openly concede that these have been balanced around the notion that you won't play more than one of them in a given match.
--------------------------------------------------
Brago, the Geist King
{2}{W}{U} 3/4
Legendary Creature -- Spirit
Flying

{W}{U}: Another target creature you control gains flying this turn.

Whenever one or more creatures you control with flying deal combat damage to a player, you get an experience counter.

At the beginning of your precombat main phase, you may exile another target creature with converted mana cost less than the number of experience counters you have. Return it to the battlefield under its owner’s control at the beginning of the next end step.
--------------------------------------------------
Rona, Cruel Successor
{2}{U}{B} 3/3
Legendary Creature -- Human Artificer
Whenever you exile a card from a graveyard or a permanent from the battlefield, you get an experience counter.

{3}{U/B}, {T}: Target player puts the top X cards of their library into their graveyard, where X is the number of experience counters you have.
--------------------------------------------------
Mina and Denn, Battle-Hardened
{1}{R}{G} 2/2
Legendary Creature -- Elf Warrior Ally

Whenever a nontoken creature with power 5 or greater enters the battlefield under your control, you get an experience counter.

{1}{R}{G}{G}: Put a +1/+1 counter on each of up to X creatures you control, where X is the number of experience counters you have. Activate this ability only any time you could cast a sorcery and only once each turn.
--------------------------------------------------
Kaervek the Relentless
{2}{B}{R} 3/3
Legendary Creature -- Human Shaman
At the beginning of each end step, if one or more cards were put into a graveyard this turn, you get an experience counter.

{1}{B/R}, {T}, Pay 2 life: Reveal the top card of your library. If it’s a land card or a creature card with converted mana cost less than or equal to the number of experience counters you have, you may put it onto the battlefield. Otherwise, put it on the bottom of your library.
--------------------------------------------------
Anafenza, Spirited Benefactor
{2}{G}{W} 2/2
Legendary Creature -- Spirit Soldier
Whenever you put one or more +1/+1 counters on a creature you control that had no +1/+1 counters on it, you get an experience counter.

{X}{G/W}: Create X 1/1 white Spirit creature tokens with flying, where X is the number of experience counters you have.
--------------------------------------------------

Thanks very much for taking the time to read about my commanders!