I've been putting this off for a long while now but it's getting in the way of writing fanfics of a character I beloved as a child.

Percy to me post TLO might as well be a completely new character because he doesn't act really like the original Percy at all.

I wouldn't have a problem with it if it would have been explained or explained better in canon as yeah Percy got his memories back. Which admittedly should cause a slight character shift of an increased irritation to the gods and Percy questioning his loyalty to them if they don't trust him in a situation where high trust is needed. Or even if it was explained as Percy's argument with Hera about bringing Annabeth meaning that she won't allow the rest of his memories to return to him. Both of those would make more sense for a post TLO, post SoN Percy but it isn't there.

Which makes it in truth feel like I'm constantly reading about a twelve year old, or even younger Percy who naively goes with everything the gods say instead of taking to them candidly like he even did back in the first book, regardless of which god it was.

The original series, we see Percy go from a twelve year old demigod who knows very little of Greek mythology and has no belief in it at all to seeing Percy as a demigod, a leader, and accepting that mortality is life. While he still struggles with some things in the later of the og five books he doesn't constantly need Annabeth or anyone for that matter telling him about it unless it obscure like needing the mothers blessing for the Styx bath or about personal life like with Hestia telling him about Luke's childhood. Percy goes from the camp runt being picked on to the demigod in charge, that even Chiron, the millennia old trainer of heroes, listening to his commands for the camp. Percy when finding out the truth about the great prophecy doesn't immediately lose it and go awol either. He accepts and decides that he'd let camp prepare for the war while he'd resort to spending time with his mother, the only true constant for love and support in his entire life, and exercise every option he can to complete the prophecy to not burden his younger cousin with the prophecy.

However with Post TLO Percy barely knows how to use any of his powers, which he arguable doesn't know the full extent of his powers at the end of TLO but he's certainly somewhat master his water control. Then we have how he acts as a whole. Percy never really likes not only being told what to do but what he can and can't do either. This most evident when him and Thalia but heads when Percy does as Hestia would likely do and share the power of leading camp in ctf against the hunt with Thalia when Chiron gave it to him and not her. But Thalia takes that and abuses Percy's peace going nature towards his cousin. As a result Percy does what he originally would have planned and made a legitimate attempt which could have given them victory. Thalia sees this as Percy usurping the power from her which mind you he gave her as a co chair not as the chair, and starts a fight with Percy that Percy likely would have killed Thalia if not for Chiron and the oracle did not stop him as he would have blindside Thalia with the wave to the back.
But post TLO percy is practically a lost puppy that listens to everyone and everyone. Which again would be fine if it was explained properly like Percy fearing his own actions because what he could do either from their time in tartarus, or more likely I think the fight in Kansas being possessed by the Eidolons, and Percy being vulnerable to Annabeth, as again post TLO Percy embers his name and Annabeth's name and that he loves Annabeth.  Why I say Annabeth is because of Percy coming out of SoN as knowing Annabeth longest according to HoO canon only, and he'd likely trust her more than the others with his vulnerabilities as he did in TLO.

All this being said. I find hard to read the continuation of the original series seeing a demigod who would back talk the olympians, since the age of twelve, who lead 40 other demigods to war in defense of their home and in defense of Manhattan and Olympus, and who would do anything, even if it meant dying himself to save his friends and family, to effectively becoming a sheep with super powerful water abilities who doesn't really know how to use them, even if he learns them the same way as in the originals by impulse and need, that doesn't really know how to do anything for himself. To me Percy after TLO is just not Percy but a new character who took up Percy's name and titles.

I mean I seen a glimpse of that original Percy in the first of the Apollo series, but that Percy didn't really demonstrate that undying loyalty to his friends when they were faced with Nero attacking camp. I get that he was busy multi tasking for college and what not but Percy Percy still would have done everything he could to help his friends. I still don't think he would have helped Apollo with his quest though but he most certainly would have done his best to help Meg before Nero's attack on camp.

Also if you ask me it doesn't make any sense why the gods didn't give the demigods anything after HoO ended. Like ok maybe Apollo needed to be punished, that could have waited till after the rewards, or they needed to recover, they were set ready to make Percy a god mere hours at most after fighting typhoon and nearly having their thrones destroyed. To me the gods are just being dicks to their kids again and Percy would have thrown that shit right back into their face when he was told not asked but told he and only he needed three recommendations for college, and that he couldn't call in favors that numerous gods already owed him to get those letters. The original Percy would have most certainly sassed Zeus straight to his(Zeus's) mother while Chiron Annabeth, Jason, and a few others would all be trying to stop Percy and remind him the gods, especially Zeus, shouldn't be trifled with.