The modem did work surprisingly well for online gaming though and routers with Ethernet sockets weren’t (yet) common in most homes so I don’t disagree with Sega’s decision not to ship Ethernet as standard. It’s just a pity those Ethernet adapters are now in such short supply.
I still play on my Dreamcast a lot. It is a great console that, in my opinion, is the first of a whole new generation of consoles based around online play. But like a lot of pioneers, it suffered a little from being ahead of its time. Plus the fiasco of the Sega CD, 32x and Saturn (all of which were actually pretty decent in their own right but shouldn’t have existed from a commercial perspective) wouldn’t have helped peoples options of Sega ahead of the Dreamcast launch either.