> there are rules in place so they can't grow too much (staking rewards decrease quickly)
I think this refers to the k factor, that puts the "soft limit" on decentralization. This I see as a barrier to entry: Ethereum 2.0 is 32ETH and that's it. Cardano has no monetary fee, but has eventual competition between pools, which is variable, likely ongoing cost. Barrier to entry is less defined, and could at some point grow beyond dollar value of 32 ETH (to become a competitive pool). Whereas Ethereum 2.0 will always stay a constant 32 ETH, no matter how many validators exist.
There might be competition between pools but also costs for them to grow beyond a point which benefits decentralization - the issue at hand.
What does it matter here if they have a harder time when none of them are incentivized to even grow to 1%? Even if they do grow, there's plenty of incentive for stakers to move to new ones on the spot. This might mean that e.g. pools will increase their costs due to the risk and stakers will earn a bit less but they still won't grow beyond a point.
I think this refers to the k factor, that puts the "soft limit" on decentralization. This I see as a barrier to entry: Ethereum 2.0 is 32ETH and that's it. Cardano has no monetary fee, but has eventual competition between pools, which is variable, likely ongoing cost. Barrier to entry is less defined, and could at some point grow beyond dollar value of 32 ETH (to become a competitive pool). Whereas Ethereum 2.0 will always stay a constant 32 ETH, no matter how many validators exist.