I thought the end was a little anti-climactic as well. Playing again I'd probably stop after getting to the wastelands, unless I was in the mood for some hack and slash.
Spoilers ahead:
I used 2 minor restoration potions when defeating the Demon of Lies (those and one for Moriendor were the only potions I used for healing in the wastelands). I don't recall how long it took, but it wasn't much longer than 10 seconds.
When I re-loaded the game to check my stats without any equipment, I figured 'no guts, no glory', cast Heaven's Blessing for the one and only time in the game (maxed it entering the wastelands to use up some skill points), and re-did the fight with the Demon of Lies. It took 106 minor restoration potions and a couple minutes, but I killed him barehanded, with no armour.
Actually, Josephine was a bigger disappointment. She kept trying to summon a death knight, but I never gave her a chance to complete the spell. She summons first, then casts a spell on the knight, then casts Blind... in that order, without skipping any steps. I didn't even lose any hit points. At least she ran away a bit several times, the first 3 Black Ring members stood their ground and repeatedly threw themselves at my sword. I had to re-load and let her complete the summoning to find out what that white sphere starting to form was for.
FYI, the publisher rushed the release of the game, so the wastelands were scaled back. With Beyond Divinity, Larian did the end of the game first, so if they were rushed again that wouldn't happen.