It's snowing outside and I want to write something so here we go.
I love debating power levels, I grew up on DBZ so that sort of thing is inevitable. My current question has been, while playing the Dissidia Mobile game, "which Final Fantasy protagonist is the strongest?" Luckily I'm enough of a clown to have what I think is a definitive answer, but it comes with a couple of caveats. This will be based purely on performed feats, which is important to make note of, and does not include MMO characters (although if I did, the FFXI Warrior of Light would absolutely be strongest). Spoilers for Final Fantasy games to follow, but they're minor.
So, in my opinion, Lightning is the strongest Final Fantasy protagonist, but not at first. In Final Fantasy XIII she's pretty powerful, but I'd say Cloud and Zidane could take a crack at her and win.
It's Final Fantasy XIII-2 where things get wild.
In Final Fantasy XIII-2 you learn about how Lightning became a defender of the Goddess Etro, and it's at this point where she becomes the strongest playable character in the entire Final Fantasy series, discounting glitches and exploits. In the Requiem of the Goddess DLC, Lightning can have 999,999 HP, and 9999 Strength and Magic.
"Okay Mint," you say. "But that's DLC. What if we discount it?" Well she only gets stronger! In Lightning Returns, she can cap out at the above, reach ridiculous levels of speed, max out her affinity with all elements, Elementaga, Holy, Time Travel, and Odin at her disposal. The girl is stacked, and in terms of feat goes on to kill, like, multiple gods.
That said, I did mention caveats, and one of the big ones is that Lightning Returns isn't technically a mainline Final Fantasy games. So what if we take away all the extra games and focus on Roman Numeral titles only? Then I'd say Noctis is the strongest character in the series.
The Ring of Lucii makes Noctis ridiculously OP. If Lightning's strength comes from getting pissed at the gods, then his comes from being "supported by them" (whether it's really support is in and of itself debatable, but nonetheless he does get his power from them). His royal arms also make him ridiculously powerful, and by XV's end-game he's more powerful than the astrals of his universe. He could stomp XIII Lightning in a second.
So that's what it comes down to, in my opinion. Just to finish it off, here's my full list of protags, excluding the Warrior of Light, Firion, and Onion, because there aren't enough feats to actually judge them:
- Lightning (God Mode) and/or Noctis
- Terra Branford
- Zidane Tribal
- Cloud Strife (especially post-Advent Children)
- Cecil Harvey
- Squall Leonhart
- Bartz Klauser