I am 100% f2p. Don't buy gem packs, even skipped the bolster forge pass (regretting that a bit... lol)
But seriously 120 energy may double the daily "required" allocation of energy, though I don't agree with that either :) but it's probably closer to 10% of the average daily usage by a f2p. And for late game players, less than that.
Everyone will complain about the low return for each run, but over time I will benefit more from 1 soulstone than 6 more dungeon runs per day.
Also ftp, and i think you are assuming 'late game' = 'keeps resources drained at all times' so are including natural regen?
At the moment i am keeping resources drained as i am for once doing a fusion, but most of the time i log on twice a day and sometimes once.