I understood it as Bitcoin becomes more and more centralized as bigger miners get more powerful. You don't know when it is happening because these few people are decentralizing their mining operations, so it would not be too obvious that they have the most power. Sounds nuts, but hashrate of Bitcoin network is steadily going up. Who are they, we don't know, but I doubt they are Venezuelans or Iranians who don't have enough money even for food, let alone buying ASICs. https://news.8btc.com/bitcoin-hashrate-increases-in-a-bear-market-investors-are-still-optimistic-in-the-long-term
Byteball on the other hand, becomes more decentralized as more witness candidates and better witness candidates will join and since they are public, they can't be the same rich person.

Think of this way, you kind of know who are the rich guys today, but you can't do anything about it, they rule the world and the banks and the real-estate and the companies. You can't even vote them off from lobbying to the government because they will lobby to whoever is currently in parliament. Just check what's happening in EU with upload filters, that's Facebook and Google lobbying result.
With Bitcoin, you don't know who the rich guys are and you don't know how many rich guys are there, there could be 10, but there could also be only 1. And you can't do anything about it, you could fork and make their hardware useless, but you probably don't get the miners because the rich guys are becoming the majority of the miners.
Byteball moves in the opposite direction, eventually there will be so many witness candidates that if they breach your trust, you replace them and if enough people feel the same, better witness gets elected.

If one day, all Byteball current witnesses are replaced then your only hope that Bitcoin is more decentralized is because you think that the big miners are not the same people, but you can't be sure. Also, if some of those people become so powerful that they could pull off 51% attack, your hope is that they will not do it because it will destroy the value of their holdings, but you don't know how much they hold BTC by that time, they could have been planning for exit or fork for very long time.

Hmm, dPOS actually totally makes sense. I am not saying don't invest into BTC, it will still for sure have nice returns, but it will not be nr1 forever.