Libertine is an Aura, which does work on its own right. However, it would be lacking if you didn’t have “game” – techniques and strategies. PSIT on the other hand, is a tool that would endow that game, it works on your personality. Think of it as preparation and training. If you have had enough time on PSIT you could use it as a refresher while using LU as the primary.
Yes, it would be less powerful, since PSITU has many other modules and cores in it; you would get less effect of LU; works the same way with other titles - Less script density would result in a more focused effect; E.G: take AM vs Ascended vs Seductress vs (major title with Ascended) OR Primal vs PS vs PSI, OR PS vs Sex Mastery vs Sex & Seduction.