I've been feeling the same issue. Both fire and lightning are getting spammed way too much now. Poison as well actually. I remember Sanji gaining fire to fight with was a really special moment and now it feels so heavily overshadowed.
There must be more to what the Mera Mera can do somehow, different colour of flames/temperatures or something idk. I'd like to see "holy flames" although Marco might be the closest to that ofc.
This is why I also don't like Prometheus and Zeus as much as I could, although Zeus had that amazing attack Nami used on Big Mom and Indra looked great too. Not sure what Hera will bring to the table yet but Prometheus is just a massive ball of flame, similar to an attack by Ace (Dai Enkai Entei) and he didn't show anything else impressive aside from that. Although being able to act as flaming hair for Big Mom and to make Napoleon become a fire sword is nice, but Zeus is still far more interesting and impressive imo.
But yeah, there's still too much fire, lightning and poison being used. We've not seen "an actual earth logia or paramecia", just a swamp fruit and stone fruit for the closest things. Clay could offer potential for an Earth fruit user too, if it's not a seperate DF either. We're also lacking in more wind abilities and an actual Wind DF too. More ice would be nice too (pun/rhyme not intended lol) but also more water based abilities somehow. Jinbei being given a way to fight with water vs Who's Who was disappointing for me, especially with how "cats hate getting wet" too lmao.
We've not seen a glass DF, nor metal or wood! Imagine a cola logia user for Franky to meet too? How crazy would that be?
At least with Yamato's DF, I'm hoping her flames will have some unique properties but I'm not sure what. Flames that cannot be extinguished (except by maybe seawater or so?) like Amaterasu from Naruto? Something to tie her in with Amaterasu from Okami somehow too?
Idk otherwise, but I feel Oda had to give her flames too to parallel her with both Ace and Kaido ironically. I love elemental abilities and fire but if she doesn't have something unique with her flames, I'll be disappointed. Hopefully some interesting unique attacks at least?
On a completely different note but also ironically fire related, what happened to Orochi setting Onigashima on fire and trying to burn it down?
And we've yet to see an explanation of King and why he's always on fire and if he does fight with fire and how too?