This is such a difficult question to answer because it's different for everyone, and it's different for different levels of different classes too...
E.g. There are GSM and ALC leves in ARR that ask for Clear Glass Lens or some other items that could be directly purchased from the crafting guilds (It's been so long, like 7 years ago... i can't remember). So, to me, that was ridiculously easy. You just go to those guides, buy a ton of stuff, and turn them in, and level up almost for free. However, it BURNs away your leves, since purchased items from guilds are NQ, so you're wasting leves very quickly.

Then there's the factor that different people do different things, resulting accesses to different mats.
E.g. Some ppl who do certain dungeons a lot will have access to certain loot drops, and if they have sufficient desyn ability, they can produce a ton of mats for free for a particular class. Some ppl who just likes to gather a lot using their Miner may have access to ores more than logs. Same thing happens when a person owns multiple retainers of the same class, such as Miner. So that means leveling BSM, GSM and ARM would be easier.

Then, there's the factor that certain leves are particular easy or cheap for certain class at certain level. OR certain Collectables being in similar situations. So some class being "easy" at certain levels may becomes "difficult" at certain higher levels... and the situation can go opposite as well for some classes. So now, which of those two types of classes is easier to level then: easy first then hard? or hard first then easy?

Then, think about how easy it is now to level up at the Firmament using Ishgard Restoration (from lvl 1 to 70-ish). It takes literally 15 min to go from lvl 1 to 50, and then another 15 min to hit like lvl 65. If you consider THIS, the little differences between the difficulty of classes don't even exist! They're all TOO EASY...

It's not a dumb question, but it's too complex a question to answer, imo. Really depends on what you do to access mats, and what you do to level up.