SEGA contributed many modern innovations in hardware and development software. Sound and their arcade hardware were top of the line in the 90s always ahead of everyone. They had games in 1996 running on arcades that look better than some PS2 games in Scud Race as one example. They were doing online gaming and cloud gaming in the 90s. DLC. First console with a web camera/Digital Camcorder/Picture Camera and email service. Phone service. Video sharing. SEGA was a huge loss. When Xbox was being developed Microsoft used Dreamcast's as a focus test console. DC is the first console to use Direct X, not Xbox. First console with an MMO. MS never filled the void SEGA left in innovation. XBL while great was still built off what SEGA built in SEGANET. Xbox has made contributions but never to the degree SEGA did.
Tom Kalinske taking the marketing to colleges and older audiences and many of his strategies are what Sony used with PS1 but they had more resources and got a wider reach. Still, SEGA got the ball rolling. Too long of a list of everything but SEGA's innovations to gaming in the 90s while not as well known as Nintendo's were just as invaluable. I mean shit, they had the Switch idea in 1995. Saturn and Dreamcast solved Analog Stick drift in the 90s by creating Hall Effect sticks which are only now starting to pop up more and more in modern controllers. Xbox Series X Dpad is just an improved version of the Saturn Dpad concept. Xbox controller in general owes itself to SEGA. Virtua Fighter is the first 3D fighting game. Tekken became the game it did because of VF.
Saying not much was lost is either pure ignorance or feigning ignorance.