Yes, that's why I always laugh every time I read "SEGA should sell Sonic to Nintendo/Microsoft/...." comments on youtube.
Sonic is their most profitable franchise. Why would they sell it, lol.
There are some who believe Sega would be better off with Microsoft. And by that I mean if Microsoft brought Sega off from SegaSammy. After all ever since Sammy Holdingsmerge with Sega, SegaSammy had redestributed Sega employees amongst other Sammy subsidiaries and enforced regulations on them to the point that Sega since then had never been the same. And it shows given the SegaSammy merged happened in 2005, with Sonic '06 being the first major Sonic game since the merge.
Meanwhile Halo games are given the budget of hundred-millions in dollars and Microsoft give them free range to the developers of these games however they think best. After all Microsoft is a multi-billion dollar industry. They probably only care if the game is good or not.
Imagine Microsoft going up to Sega and saying "We want a Sonic game exclusive to PC and XBox. Here's a few hundred-million budget. Now if you excuse us, we literally have the rest of the world to run."
But as you said, Sonic Team makes millions for Sega and SegaSammy won't relinquish Sega.