This is true for every part of the AST toolkit: people haven't taken 5 minutes to think about how it's best to use the spells. Whenever I see some bitching, people are giving examples of how they use skills and it's just wrong. Some even complain that the cards are not useful because dps is not going up that high. My bet is that they thought that dps was gonna jump from 6K to 7K from cards and that they would be carried by buffs and wouldn't need to improve their player skills. Back when my group was having trouble meeting the DPS check in Bismarck EX, I told my group that they need to get good, because they can't rely on cards to meet specific DPS checks; AST was never designed to carry a group with poor DPS.
On MP management, I usually use LA when 20% of my MP is spent; sometimes I use it earlier when I need to spam. It's back by the time I need it again and my MP is usually floating around 7K-9K. I also added more piety to my build, which is basically a PIE > SPEED=CRIT build.