When Stellar started, they were all about 'Quorums'; trying to imply that this was the secret sauce which would allow it to scale unlike any other blockchain. I initially thought that quorums were like separate shards but after asking around years ago, I found out that it was not the case; all transactions pass through all nodes; exactly the same as a plain old blockchain. These days they barely even mention the concept of a 'quorum' because it was never anything more than a scammy marketing tool.

I don't know too much about Cardano so I won't criticize too much but when I skim-read their whitepaper about 1 year ago, it sounded over-complicated. This is a red flag for me. Also, they are yet to implement smart contracts; so there is a long way ahead. I don't like that they keep bragging about their all-PhD team. In my experience, PhDs aren't good at delivering good developer experiences or limiting the amount of complexity.

I wouldn't say that XRP/Ripple is a scam; but only because they don't make it a secret that they are essentially a centralized crytocurrency with multiple nodes for redundancy. But some could argue that they are a scam based on the fact that they don't solve any of the problems that a cryptocurrency is meant to solve (this critique pretty much applies to all top cryptocurrencies BTW; they don't solve any significant economic problem aside from upholding the status quo; the opposite of what they claim to do).

>> So it's a scam because it doesn't exist yet and it's planned on the roadmap?

It's scammy because they sell it as if it already exists, but it doesn't.