I don't think I have used that Briess Munich (which says it is a 10L version). It should not be a caramel malt, but it will add some malty character that can give an impression of sweetness. The combo of Maris Otter + Munich + Crystal was probably a bit overloaded on the malty malts. I like an Irish Red with about 5% Crystal 60, 2-3% Roasted Barley plus Pale Ale Malt.
Your pre to post gravity drop is quite a bit for a 75 min boil (1.054 to 1.074). You might be boiling too aggressively. That can also contribute to malty and sweet characters.
This article seemed to have a good explanation of BU:GU ratios (Bitterness Units to Gravity Units):
BU:GU Ratios If the 25.8 IBUs is correct, then your 0.34 ratio would push this beer a bit out of balance.