It's only easy if you have better than the leveling gear the typical player leveling crafting will have. Not every player can afford to spend 75k gil per HQ piece of gear from the MB. Most will be relying on vendors for NQ gear because what used to be a fairly large supply of NQ gear from quest rewards showing up cheap on the MB has disappeared.
As for material costs, they're only cheaper for the level 20/40 recipes (I'll go more into that below).
Scrip gear works fine for leveling, not to mention the player is again earning XP as they earn the scrip. I wouldn't go full scrip for level 60 since there is no shared left side gear except belt but certainly the tools and accessories are worth getting. It's more cost effective than paying out of pocket for gear then paying out of pocket for recipe materials since you only have to pay out of pocket for the recipe materials.
Someone who is using level 20 gear to get all the way to 80 via Firmament is going to be at it a lot longer than someone who stops to get gear along the way.
Have you paid attention to how much Skybuilder Scrip is earned as you level? The amounts are small compared to item cost and the MB has been flooded with the majority of those items, driving prices down. It is not a good way to earn scrip to make gil until you hit 80.
The same can be said of Skybuilder scrip. It makes more sense to have your leveling serve a double purpose. If you're going to need the yellow scrip later, may as well earn it while you level.
While the Master books aren't technically needed while leveling, some players want access as soon as possible for the primal weapon and housing item recipes they contain. How disappointed my friends were to find they didn't automatically learn those recipes, and what they needed to do to get them would have also earned them as much if not more XP.
That's no longer true across the board. Normal materials have dropped down significantly in price due to changes this expansion. Firmament material cost will generally be lower for the level 20 and 40 recipes. It takes a big jump when you hit the level 60/70 recipes.
Using the level 60 CRP recipes as an example and current Coeurl MB prices
Firmament -7500 gil
Splendors - 4500 gil
Leve (Beech Rod) - 3600 gil
There will be some variations based on which class you're leveling but from level 60 on, the Firmament recipes tend to be the most expensive if you are not gathering you own materials.
There are a lot of assumptions being made about leveling based on what things were like in the past. Few are bothering to take a look at what things are like now. The marketboard is not what it used to be. The belief that the Firmament is the better way to level has driven the prices of those materials up while the prices of materials for normal recipes have fallen down thanks to lower demand and desynthesis changes.