tanks beat burst if they can stick to them
burst beats adcs if they can reach to them*
adc's beat tanks if they can maintain distance from them
And even my simplified version doesn't cover all the relevant categories that comes into play for the "rock, paper, scissors" scenario you describe, but mine makes what I'm about to say easier to understand:
a class becomes unbalanced when certain factors that contribute to this rock paper scissors become irrelevant.
Tank/Juggernaut Meta: These guys could dish out enough damage to the point where they essentially didn't need to stick to targets
Burst Meta: Their burst was so strong and fast that
a) the needed window of space they needed to perform their job was too small to the point that it was oppressive or
b) their burst was so strong that even tanks were irrelevant to them
ADC Meta: Their raw damage and abundance of penetration minimized the need to avoid tanks because 60% of their armour was negligible anyways. Many adc's possess such amounts of burst that they can go toe-to-toe with burst characters while maintaining a large threat to tanks.
And you exaggerated things wayyy to much.. No one (who isn't salty or stupid) wants dps characters gutted, they want them managed. They don't want tanks to be nearly dead by the time they walk up to an adc that has been standing still. Burst characters don't want to be out-bursted by a Vayne Q -> Auto -> 1200 crit in the mid game. There are some extreme outliers in the adc class right now that feel wayyy to oppressive and provide aspects to the game that sit outside their class's parameters.
Kalista was a great example of this. She was really one of the earliest outliers of the dominant adc class where she provided too much and excelled at too much to be considered healthy. Free kite, free engage, free burst, free dps, free displacements, free team-saves.
