As you pointed out, the day-of availability of the most popular T1 LL should effectively be the same under LL-MP. However, the secondary T1 LL availability could suffer because I have a feeling the "Country Bears Effect" might come into play.
One of the many interesting things in the Defunctland FP+ video was that Country Bears had long waits when it first opened because it was designated as an E-ticket and uninformed guests just assumed that meant it was one of the best attractions. Once they changed it to a lower ticket level, the lines went away.
I think a similar thing may happen here with the LL tiers. The most popular ride will be unavailable by park open just as it often would be under G+. However, the availability of the remaining T1 LL could be affected. Most of the people using this won't necessarily be "power users" that know all the ins and outs. When those guests are making their pre-selections, once the most popular T1 runs out, the Country Bears Effect kicks in and the uninformed guests will select a T1 ride that they might not have selected day-of with G+ just because they assume T1 means "best rides," or because they incorrectly assume you have to choose a T1 LL.
This would mean that the day-of availability of the secondary T1 rides would be negatively impacted vs. G+