In general I see LUC and St. Mary resume to be similar, so then you look for differences and here is where I see St. Mary resume is superior:
1. Superior Q1 victory (Gonzaga)
2. Superior Q2 victory (50 RPI win vs 87)
3. Predictive metrics better (24 vs 55)
The biggest thing that LUC will be held against them is their non-conference schedule. You have little control over conference you play in, but you do have control of non-conference.
LUC non-conference SOS = 258
St. Mary non-conference SOS = 178
If I was St. Mary I wouldn't be feeling very comfortable with their position right now.
The one thing LUC does have going for it is they have won their conference title. Sometime the selection committee does put more weight to that.
How to game RPI = schedule the best teams that you know you can beat. But that may or may not work next year depending if the NCAA actually moves away from RPI.