I was saying that because UK is well known to be a SEGA/Sonic country. But maybe it's becoming that less with time as well. I agree with the comparison though. I just feel like SEGA is ruining their brand and they may not have any iconic IP's to sell anymore if they keep it up like this we'll only see great investments (like creative assembly and relic) making them money.
Even on the Gamecube Sonic's debut was modest, what really helped Sonic's popularity skyrocket back then was Sonic X. Just to put it in perspective how much of a big marketing boost it was for SEGA, Sonic X was one of Fox Kids (I believe that was the network?) most successful animated show until the rebooted Teenage Mutant Ninja Turtles cartoon. It was massive and if Sonic Boom gets similar sort of ratings, expect the blue hedgehog's popularity to jump start again.
Also depends on how much stock you want to give to the mobile market, Sonic is a massive success there with Sonic Jump having over 8 million downloads and Sonic Dash with over 20 million downloads.
As for SEGA, they've never had big sellers sadly, if they did they would not be in the situation pre-Dreamcast or post Dreamcast. Infact it can be argued that they are more successful now than they have at any point excluding the Mega Drive era, they have never had three consistently 2 million+ sellers before.
Sly and Ratchet in particular move paltry numbers by comparison.
Ratchet and Sly are good sellers, what made you think otherwise? Ratchet even does over 2 million in sales usually.