This is at the end of the day still a game about chance. Having indefine upgrades removes the whole chance aspect. Plus having a max makes it like you've reach an end point.
To the "bad" balacing: Are you upset that the percentages of heads doesn't feel like what it actually is? If that's the case then I'm very sorry but that's just plain statistics and chance calculations. Sometimes you get streaks upon streaks of heads even with 80/90 or even 95% head chance. Just because that number is high doesn't mean it isn't unlikely to happen.