Titles are supposed to be descriptive for the purposes of clarity for players. Think about it, without knowing anything about Rek'Sai, what does the title "The Scourge of the Desert" tell you about her? She's something bad and the's got sand stuff going on. Lore wise that's good, but gameplay wise that's inaccurate! Void Burrower is much more descriptive when looking to just be upfront and clear; She's a Void creature and she burrows. That's Rek'Sai through and through.
This is why Azir's title is the "Emperor of the Sands" and not the "Emperor of Shurima". What does Shurima mean to anyone who doesn't know the lore? Jack-diddly-squat. Emperor of the sands tells you he's an Emperor and he's sandy.
Kalista is the "Spear of Vengeance"; she uses spears and is all about vengeance - this is Kalista in game. "Lady of Vengeance" is Kalista in the lore.
Sion is the "Undead Juggernaut". He is undead, and he is a juggernaut, these are indicative of what Sion is like in game.
Tristana is the "Yordle Gunner". She is a Yordle and she is a gunner. It's pretty much exactly like her old title except Yordle and not megling. Again, this is Trist in game.
Bard is the "Wandering Caretaker"; he's someone who takes care of people and he wanders around a lot, these are a part of both his character and his gameplay.
It's not about making the titles incredibly interesting, it's about giving a sense of what this champion is clearly. That seems to be the trend at the moment, and it looks like it's going to continue. Look at Gnar and ask yourself; if you're just looking at Gnar for the first time, you don't know what the hell his title means in any way shape or form. "The Missing Link" means nothing from a gameplay angle. Lore wise it's totally accurate and we know this, but gameplay wise "The Missing Link" doesn't mean a whole lot.
Also who ever said champs are restricted to one title? Sion was once the Hand of Noxus like Darius, Kalista's known to some as the lady of vengeance.
the "Loose Cannon", and then 
the "Crazy Bitch".
