It's supposed to be HOT water, not lukewarm... I have my water heater set to 150F because it makes the hot water last longer, especially in the winter when the incoming supply is barely above freezing, but that doesn't make the tank bigger.

I was surprised at how cold "hot" water actually was. I thought it was 60-70, but apparently what feels "hot" is around 45-50. Especially for me, that finds anything beyond my shower's "middle" heat as uncomfortably hot, I must be showering with around 40 C water, which is basically "hot day" hot.

Then again, I grew up with thermostatic valves in the shower mixer, and a "child safety" latch to restrict it to even less hot water in normal use. I don't see why putting the mixer in the water heater is that different.