Soul EruptionR Instant
Add R to your mana pool for each damage done to you this turn by sources you control. After beholding such a phenomenon, one would be convinced to call it an Act of God.
Keeper of Balance1W Legendary Creature — Avatar
Whenever a permanent enters the battlefield under a player's control beyond the first of that type, tap that permanent. It doesn't untap during its controller's next untap step. Ageless experiences could only hope to teach you an ageless lesson—those who disrupt the balance are doomed to be claimed by it.
The existing mana base makes soul eruption broken beyond repair. In smaller formats its more interesting but probably leans to heavily in either underwhelming or broken.
Keeper of Balance, if you drop hexproof and reduce to 1/3 or 2/2 then the any permanent text works well. If you don't then its overpowered either way. Hexproof and a huge butt on such a low drop is an absolute nightmare on any deck trying to kill you fast. Add in that it nerfs fetchlands and cripples mana ramp and it quickly reaches oppressive territory.
Soul Eruption makes sense, its wording just needs to be tweaked slightly to be in line with how rules text is phrased. Its an odd effect, and 1 mana abilities that make large amounts of mana are always dangerous in older formats, but at least the hoop is difficult to jump through.
Soul Eruption R
Add an amount of R equal to the amount of damage done to you this turn by sources you control.
The problem that keeper has, as written, is that the tapping the land is a triggered ability, meaning that the player with the land coming into play can just tap it for mana in response. The wouldn't be able to hold up the land for a counter or combat trick, but they can still use it to cast a creature or sorcery on their turn when they play it. You can instead simple have the land enter the battlefield tapped to avoid this.
Keeper of Balance 1W
Legendary Creature — Avatar
Other than the first land that enters the battlefield under each player's control each turn, lands enter the battlefield tapped and don't untap during their controller's next untap step.
The effect honestly doesn't do a huge amount, since fetch lands can be used on opponent's turns and most other abilities that put extra land out already put them into play tapped, so it will slow down ramp a little but not much. The bigger problem with this card is that and 0/5 hexproof is very non-interactive and, at two mana, will drive aggro strategies out of the meta very hard. Either the cost should increase or the toughness drop a lot so it is a significantly less effective blocker.
Overall these cards underestimate their power level some, but aren't inherently broken and work within the rules. The effects are somewhat niche, but at least drive interesting deck building decisions.
Keeper of Balance doesn't specify to that turn which makes it horribly broken in my opinion. It means that your opponent is having every creature they play tapped for 2 turns making defense impossible and lands become use it immediately or lose it for two whole turns rather than just the following turn. If you're on the play your opponent has only 2 mana at best on turns 2 and 3, and 3 at best on turn 4. Of that one of it must be used as the land if played. In addition it's going to be a miserable card to play with. Slows the game down drastically and absolutely punishes decks interested in anything beyond putting cheap permanents onto the board. If it's just meant to be the first of that type and be a fetch land punisher then I can get behind the card but not as written now.
As for Soul Eruption I agree with user_938036 it is either useless in smaller formats or among the best rituals in larger ones. I think that's actually fine but I just want to make sure you realize how powerful it is.