To be clear RandomX is great, it’s not surprising that other chains want to adopt it but the flaw has to do with the skewed economic incentives generated by merge mining. It’s just an attack vector that is out there and that nobody had exploited until now. P2P is great as well but miner seeking to maximize their profit in the short term are incentivize to merge mine the most profitable auxiliary chain. I don’t know if that’s enough to allow a more sophisticated attacker to achieve a 51% attack but is this a risk we are willing to take?

A 51% attack on PoS would actually be more visible because the price would skyrocket as the attacker attempts to buy all the supply. The attack isn’t practical. With merge mine, an attacker can create its own bogus chain with little token supply on exchange while holding huge share of the premine. They pump their coins, incentivizing hashpower to mine their chain while pumping their bags at the same time. It just requires good coordination, marketing and network. No need for massive investment.