Yeah I also think they should have prepared some stuff in advance before telling us,I mean looking at all the lores that didn't mention the IoW they probably planned all this for quite some time(and other-world champs were on the retcon list for quite some time anyway),so it is really glaring to hear that they actually haven't preprard anything for these champs.
However I disagree with you about some stuff of characterisation,I mean Twitchs lore is unfitting?Is it really so off to think that if someone stole twitchs stuff,that he would follow them and get it back?You forget that twitch had always been quite crazy.
Azir and Yasuo do have quite some characterisation,Yasuo was once an arrogant and battle searching samurai,but that caused him to fail his mission,he accepted that he did a mistake,but wasn't ok with being blamed for something he didn't do.Hearing his VO it has become clear that he isn't as arrogant as he was before(sure he's still a bit cocky,but thats about it),he feels genuine remorse for his actions.
And when Azir was announced almost everyone thought he'd be evil,because of his vanity and obsession with shurima,it was not off to see him as some mad conqueror.But in the end he was more like a noble dictator.He was naive in that he didn't realise Xeraths growing hatred for him,he couldn't understand how it was for Xerath to be a slave,but that didn't make him a bad person(as seen when he gives Xerath and all the slaves their freedom).His whole family died and his nation is in utter chaos,all because his best friend betrayed him,he is completely broken on the inside because of this.
I can see your point about Kalista and gnar,riot wants to tell stories step by step and well these lores are nice and fitting introductions.
But the problem is just that we don't want introductions,we want the main parts,the important stuff that gives us a deeper insight into these characters and with riot failing to deliver some lore recently(and generally slow releases of lore) it simply is a bad move to give us just these small tidbits.
However people tend to generalize "new lore"=must be worse than anything of the old lore.
I mean seriously the old lore also had fails like these(just look at hecarims lore which consists of hecarim running to the league and joining it,what does it tell us about him?He is an evil guy from the shadow isles duh.Same goes for Mordekaisers,Evelynns or even Garens lores).So I don't understand why it is suddenly such a big deal.Both new and old lore have their highs and downs,but at least in the new lore it becomes clear that riot thought a bit ahead and leaves some stuff in the unknown on purpose(unlike in the old lore where it became evident over time that they simply didn't think some things through)