It’s kind of like this:
The best score you can get on a 5* (A+) will always give you less loot rolls than your worst score on a 9*. Higher is better here.
(You get a certain number of potential loot drops based on the number of Titan you defeat, and also based on the grade you get on that Titan, which determines your number of loot rolls; see the handy link @Zephyr1 posted.)
A 5* A+ Loot Tier counts as XIII (8), which only gives you two rolls toward ascension materials, vs 9* C Loot Tier IX (9) and above which gives you three rolls, per the link. (Please read the link carefully; RNG rules here as elsewhere, but I’ve enjoyed much more ascension material success at Titan’s 9* and above.) 
Edited to answer Bud.