I think an important factor is the 1660 is 6gb card while the 5500xt is a 4gb card. So 4gb limits your ability to mine different coins. If you're only talking about mining etc than understandable.
I think he talks about the 8 GB version of the RX 5500 XT,as it would be stupid nowadays to buy a graphic card with only 4 GB of VRAM which is good only for ETC,UBIQ,MUSIC,PIRL etc.I believe also to get the 1660 as even though a 6 GB card it has higher hash rate at KawPow algorithm 10.5Mhsh against 7.5Mhsh of the Rx 5500 XT 8 GB in case Ethereum go PoS as it is planned.