I mostly focused on Sega CD compatibility as I figured most people interested in Genesis games would have already owned a Genesis so they wouldn't have purchased a new console for Genesis games, being able to play Sega CD games when not previously owning the Sega CD add on due to cost would have been a real appeal for people at the time. Though thinking about it more I do see the logic in Genesis compatibility as that could draw SNES fans towards it when upgrading to the new generation, and even with existing Genesis owners I didn't consider the potential cost saving as someone could sell their existing Genesis console to help pay for the Saturn without losing the ability to play their existing library.
It's either the Saturn that lost the most or possibly the Atari 5200 at launch. The Atari 5200 did eventually offer a device for backwards compatibility but not at launch, and early systems weren't compatible with the 2600 cart adapter without modding. The Atari 5200 might have succeeded if it was compatible right from the start.
With the Dreamcast it mostly comes down to personal taste, I personally will always say "it sucks" because of how disappointed I was with the various games I played on it, and the hardware issues I came across with various consoles like random resetting and the general awkward controller. It's really Shenmue that disappointed me the most and convinced me to sell off my Dreamcast stuff. There's still decent titles like EGG and various import releases, but just about anything else worth playing would have been ported to other systems in enhanced versions so today there's little reason to prefer the Dreamcast versions over the ports. I do exaggerate about the library partially as a joke, but I do still think it's close to the truth as well. Most games really weren't what most people wanted to play at the time. People blame piracy for the Dreamcast's failure, but that didn't kill the PS1 as that succeeded extremely well even with extensive piracy also affecting it.