In general, I find the writing for TKC lackluster compared to the PJO series. They introduce a lot of new characters and it feels like the author expects us to just like them without giving us a reason to like them. I definitely think it's the difference between 5 and 3 books but even in 3 books, there are pacing issues present in TKC.
The two most glaring issues I have with TKC is the romance and the cultural issues.
1) Romance
It's the forced romance that bugs me. Sadie is 12-13 getting in relationship with Walt and Anubis and then the author fixed the love triangle by making Walt the host of Anubis which for me was too convenient. It's Schrodinger's age gap! To be fair, I think that this aspect is really due to amatonormativity not being written well.
Zia and Carter are cute though I wish Zia, the only actual Egyptian that's a main character, appeared more in the books and had more personality.
2) Cultural issues
This stems from 1 moment in the first book that really stuck with me. Walt and Sadie were talking about a sign they saw and it said Cold Bebsi. Then they explain how there's no p in Arabic and how Pepsi becomes Bebsi and so you need Bebsi with your bizza//Brobably as dialogue.
I know it's supposed to be humorous but as someone who has been made fun of for speaking foreign languages as a tween, I guess this struck me as culturally insensitive. It may just be me though.
I still like TKC it's just not as good as PJO to me and this isn't meant to be hate or anything!
Would you be interested in writing fics where PJO characters meet their Egyptian counterparts?
I haven't written anything strictly for TKC yet, the closest I have is Pearl in the Nile which is a crossover with PJO. I think Rick did a decent job introducing Sadie and Carter, we got a nice build up to them. But the characters in book 2 were a bit jarring. Honestly, I get what you mean on the 5 vs 3 book series because I think an extra book to introduce the new members of the Nome would've been good.
Yeah the romance is wild, though first poly ship technically lol. I think he lowkey forgot how young he made Sadie, he definitely forgot Walt's age since he changed it in the same book Walt was introduced (from 14 to 16).
Zia NEEDED more page time oh my Gods.
I think the language thing was him trying to introduce the differences in languages with different letters. Ironically, this could have also been done in the Greek books with how the Greeks used hard K sounds instead of soft C sounds for many works (Kyklopes vs Cyclopes for example). Shame it wasn't, but I think he outright doesn't know that.
Anyways, I dunno if I'd be interested in such a fic outright but I do have Pearl in the Nile where Percy will eventually interact with the Egyptian side.