Now on topic, I wonder if samurai and watnotsabi use the same technology?
They use different technology. Samourai uses Whirlpool/ZeroLink[1] while Wasabi use WabiSabi[2].
What exactly is needed to run such a service? honestly if both wallets are completely open source, then there is no need to point fingers and have such dramas, one could simply fork the wallet and start a new service, a better one.
At bare minimum, a server and ability to follow guide about setting either coinjoin software. But gaining people's trust and liquidity to perform CoinJoin isn't simple.
[1]
https://docs.samourai.io/en/wallet/features/whirlpool[2]
https://github.com/zkSNACKs/WabiSabi