OT: Maul could lose to Grievous in Legends. I know that may seem like lowballing but I just don't think his offensive style is well suited to deal with Grievous's physical stats even if the Sith is technically more skilled. If he does make it pass Grievous he loses to Kenobi. They were more or less equals in TCW and RotS Kenobi is more skilled and powerful than his TCW counterpart.
TCW S7 will be = RotS
Maul defeated TCW S4 Kenobi,
Then Maul has grown more powerful in TCW S5; manhandled Savage Opress, and dealt with amped TCW S5 Kenobi by ragdolling him.
We know Kenobi was always amped against Maul due to Qui-Gon's death, but Maul is a more skilled fighter in normal circumstances.
Also yeah, saying that Grievous, as a jar'kai user, can win against the master of Jar'kai ; Maul is a stretch. Maul proved himself against stronger jar'kai users such as ; Ahsoka, amped TCW S5 Kenobi, Savage Opress and 3 Inquisitors.