on-element boost isn't that much outside of the cases where you're actually punished for being off-element - the only one that matters is GW, which is also incidentally pretty much the only meaningful 'end-game' competition currently, which makes it matter the most.
Outside of that, if you're capable of hitting the damage cap off element through various memes, then the only advantage on element gets, damage-wise, is critical hits, which again isn't that big.
On top of that, there's a lot of unintuitive things to damage racing that just don't make sense but help a ton, primarily in that your level of eSports directly correlates with the number of windows you have open of Granblue for the same exact raid. A single turn of auto attack animations can take 10+ seconds, but you can actually attack again after roughly 4.25 seconds - so having a second window open is necessary for maximizing turns taken, and some super serious people do a third window.
Realistically, your F2P element ranking is dependent on the characters you have, some of which are insanely necessary for synergy. Assuming you get the worst gacha draws in the history of ever (like Rdy - renown for having only pulled De La Filles in his first half year of playing), the ranking probably looks like this:
Magna:
Water > Dark > Earth > Wind > Fire > playing a different game > Light
Primal:
Earth > Water = Fire > Dark > Some fuckboy Grande Order team with all HP Skills > Light and Wind
My reasoning for this is that Uno and Quatre for Water are absolutely godly - if the grind to 5* both of them is taken (which is as shitty for a paying player as it is for an F2P player) then it stands far above the rest of the elements. Additionally, Water has ridiculously good Idols from events, and Story Kat who is an SSR cosplaying as an SR. Dark is up next because even with bad gacha luck, getting anything Dark means you probably pulled a decent attacker, as well as having a good GW character, bonus points for having a good enmity grid. Earth is next for decent GW characters, easy magna grid to farm, and good idol character. Wind is okay because it has a good enmity grid but without specific characters it falls short very quickly end-game. Fire also needs specific characters and its magna grid still kinda sucks. Pretend Light doesn't exist if you're F2P.
For Primal: Earth has a good primal grid that is reasonable to farm which can put 5* Sarasa to work. Next up are Water and Fire - note, Water is the best Primal grid if you have infinite money, but without infinite money it's only a good Primal grid that is carried by absurdly good GW characters. Dark is also a good Primal grid, but it requires a lot of money or a hell of a lot of grinding and why wouldn't you just do Magna?
These rankings change depending on what kind of characters you pull, mostly whether Fire and Dark are higher than Earth and Water for your layout.
Light is fucking garbage just don't do it, save yourself the trouble. It's the worst grind in the game and doesn't even manage to do good damage, and then you're still dependent on good characters anyway. Your selection of weapons is so dull and boring that your Magna grid and your Primal grid are exactly the same.
Wind doesn't have a Primal grid.
