Featureless Coastal tiles have never been
that good in civ. Their peak was probably civ4 - running a Financial trait with the Colossus you could get 2

4

tiles, which was nice, but not really growth. And in Gods of Old the Cathedral of Enki acted as a second lighthouse, giving you 3

tiles.
In contrast, sea resource tiles have usually been pretty attractive thing.
In civ5 coastal starts were optimal because
1) Trade route bonus yields
2) having 3 sea resources was basically a game winner for growth. Just a lighthouse gave you +2

and +1

on fishing boats.
In contrast, in civ6 sea resources are pretty mediocre. You have to build a harbor first,
then the lighthouse to get a food boost. No production until the shipyard. Even the food is a lot worse than it used to be. As someone pointed out, an improved fish tile is essentially a blank wheat tile in terms of output. That's pretty mediocre.
Sure, coastal cities get easier early access to extra int'l route gold, but without the boost to trade route

and

like civ5 had, they simply aren't the domestic trade powerhouses they need to be to keep up with land cities.
Then they get hit again: We cannot build many districts or wonders on water, and even more importantly,
you cannot chop for production on water tiles. There's no source of hammers.
IMO if they had domestic trade route efficiency bonuses too, then players who build a network of coastal cities could supercharge their internal trade to compensate for the other weaknesses. A land empire couldn't build 1 coastal city to reap the same reward like they can with int'l route gold, because there's no sea route from that single coastal city to his other cities.