To open this, I should write why it's "not reasonable" because many might not understand why. But there are spoilers in this reasoning, simply because we know of future series requirements. There's also spoilers in the solution that I think is the best here, too.
Due to the fact that the next big Zig 15* weapon series uses materials that Steel needs AND is the best 15* series available on JP, no one with this knowledge wants to make a Steel. It wouldn't be an issue if the materials in question weren't either time-gated or rare, and other materials are quite expensive because they also are used in future units.
On top of this, the existence of Plus Potentials for Atlas Ex, Trailblazer, and Rivalate heavily hurts the desire to make Puras and Steel weapons. As a matter of fact, there's almost no reason to make a Puras or Steel weapon of a type you already have a Rivalate of because Rivalate will outperform it. (and there's literally no reason for the Harmonizer, lol)
With the above in mind, though, why would someone want a Puras or Steel wepaon? The main reason is either for Camo purposes (main class, generally) or to have access to an S5 S-Grade Augment which has enough power or utility to outweigh using the other options (alt characters or classes, generally speaking). For me, it's a bit of both. The S5 might not make up for a power difference either in some cases, but it can change how you play -- and this is important for building muscle memory while you play the class.
We do have the Fluxio series coming potentially... but that's even more reason for Steel weapons to not be so heavily gated.
By this point I assume you don't care about spoilers, so lets get into it.
Steel Weapon requirements (includes the materials to make Puras):
- 3 Different +35 weapons (Dim and 2 different 15 stars)
- Lumincrystal Grania x8 (MAJOR ISSUE HERE)
- Luminfragment Emel x700
- Pure Photon x200
- Ultimate Booster x20
- Module - Varuna x25 (tradable)
- Module - Mitra x25 (tradable)
- Module - Exegul x50 (tradable)
Cras weapon requirements (only includes mats for 1 Ayer):
- 170 Fragments from future Urgent Quest
- Divine Eyestone (similar to a Rivalate Key or Chronostone)
- Lumincrystal Grania x4
- Luminfragment Emel x200 (part of Ayer, you need 6 unless you use Enhance Caps)
- Diard x50
- Ultimate Booster x30 (Ayer)
- Other various bits such as Emerard, Excubes, Class Excubes.
Lastly, Cras units require a bunch of modules to make -- they require the same amount as making a Steel weapon, but with the addition of Shiva Modules being required.
The big elephant in the room is the Lumincrystal Grania requirements. These are very very rare materials from Divide. The vast majority of Grania's come from the Divide Medal shop, which only lets you buy 4 per month. You also get 2 from a title. To explain how rare these are, I've only gotten 1 Grania drop in well over 60 million Divide Points (across JP and Global combined).
Steel requiring EIGHT of these is nasty as hell when we know we need them in the future for a better weapon series -- and most people can't even make Steel for at least another 2 weeks right now. By the time they'll be able to make it, we're far too close to the next weapon series to even consider it.
The Luminfragment Emels are farmable but kind of excessively, especially due to Plus potentials using them as well. It's very easy to find yourself low on these, and you even need a bunch to buy your monthly Grania. And as mentioned before, the existence of plus potentials also hurts the reasons we have to make Steel, as things like Rivalate match Steel at bare minimum in terms of damage. The same can be said for Ultimate Boosters -- very farmable, but can add up quickly especially on Ayer. Puras doesn't really require many of these though.
The Modules are tradable, but knowing that they're used for some of the best units in the game hurts a bit -- and the prices on ships have been quite high surprisingly. Some people are probably making some of the weapons in the Divide Medal shop, I guess, which also use Grania's...
Overall, something needs to be done about the Grania requirements. Due to the accelerated pacing and the existence of Plus Potentials, the requirements to make these weapons makes no sense whatsoever -- they're completely unjustifiable. Having to spend materials that are time-gated that we know for a fact will be required for THE BEST weapon series in the extremely near future hurts people's desire to make said weapon at all, especially because of the amount of these time-gated items it asks for.
While writing this I think I found a solution that addresses this easily, but would require an announcement or potentially confusing players by showing a weapon series before they can make it. Removing the Granias from Cras requirements entirely makes sense, as Cras is already gated by the Eyestone anyways. There is no reason to have a material requirement that also gates another 15* series that people use, and lowering the Emel Fragment requirements on Ayer could be argued too. However, even with this, I still believe the requirements on Puras and Steel should go down by AT LEAST 50% each pretty much across the board -- we simply cannot get the materials required in any reasonable timeframe even with this change. I don't think removing the Grania requirement on Puras would do any harm either -- hell, Puras literally drops from content in the near future even, even if it is very rare.
The Divide Medal Shop might need to be looked at too (and I'm sure SEGA has the ability to refund materials to those that bought these weapons) in the same regard, but I haven't thought about that part yet other than a Sword that is missing for some reason (it was part of the initial 6 weapons in that shop, so it makes no sense that it's missing on global). I do know the weapons there drop much more commonly once we get the Divide expansion but that's all I know.
As mentioned before, these weapons don't really invalidate Trailblazer or Atlas Ex, both of which are very strong with their plus potentials and have utility attached to them as well -- so it'd be nice to actually have these series be accessible to players.