They are in a sense and thats what SEGA west has done. The new restructure has SEGA America basically as a localization middle man and that is probably the best.
The issue is SEGA Japan hasn't had a long series for awhile. Right now they are still pumping Sonic (which has gotten its own brand team here), Yakuza, Hatsune Miku and Puyo Puyo (due to its more recent success they have made their games bigger). The issue is SEGA hasn't created new brands for a new generation and this generation is quite a ways in. This is why it seems like 'meh' in terms of content. IF SEGA was serious they would give each franchise they created for a new generation a fair chance which they are known for not doing. For example the first Yakuza localization was a mess and the team hyping it kept telling people it was a Japanese GTA, after that they kept quite about bringing back other games and never gave it a full push it deserved.
Hatsune Miku had the same issue, Western SEGA wasn't keen on pushing it forward and same thing happen with Binary Domain (brought out to die).
This doesn't just happen with SEGA West vs SEGA Japan tho, SEGA America didn't advertise Isolation compared to the marketing push they gave Colonial Marines because Marines was a game they were doing and Europe's Creative Assembly worked on Isolation.
SEGA isn't unified, even now. Look at GamesCom, its all PC titles which is sad cuz they have a Mania, Yakuza 0 and other demos sitting right there to show off to a new audience.