1. Enma can easily defend himself, he protected himself and defeated 1st &
2nd Hokage, plus he can turn into the Adamantine Staff which is pretty much impossible to harm. Now tell me is Enma not capable of protecting himself and Hiruzen?
2. Yes Mangekyo Sharingan is powerful, and yes he has 3 eyes, because of Hashirama's gene's he was capable of doing that. Hiruzen can easily counter Izanagi by just keep fighting him. lifes will be gone fast, and Shisui's eye won't work, since Enma would be there too and would support each other o not getting into genjutsu, also Hiruzen knows well of Sharingan and genjutsu and is capable of protecting himself.
The only time we saw him fight, he got out of genjutsu pretty much unharmed, and he could counter all of 1st & 2nd & Orochimaru's moves.
Hiruzen wins with mid difficulty.