Do you think jump infantry in the periphery are a lot rarer than they are in the inner Sphere?
Current timeline? No idea. Before the time jump? They're everywhere.
The Periphery nations aren't that backward in the infantry field, quite the oppossite since they rely more on conventional forces instead of mechs.
Jumpers are simply rare in general. It's simply so much easier to raise a grunt or motorized infantry. Each faction has usually a single cannon jump school, maybe a few more; but almost every planet has the means to train regular infantry, and most do. No point for a planet to send thousands of recruit across the empire, just to fill up its own planetary militia.
I would say they are more rare in the Periphery because everything "advanced" is more rare in the Periphery, but as Sol says they are NOT common in the IS either.
The FC-RCT's have them as 1/5 Regiments but that is only in the RCTs. They are the least common type of infantry & are rarely found outside of RCT deployments.
The question then is what is "Rare" outside of RCT deployments? Would you say Rare would be 4 RCT Jump regiments for every 1 Non-RCT Jump regiment? I'm honestly not sure but that sounds like a good figure.
Some quick stats.
There are 14-ish Infantry Regiments for every Mech Regiment in the AFFS Line Forces.
Half are assigned as individual regiments, the other half are assigned to RCTs & Full Infantry Brigades.
So if we multiply that by 4 RCTs we have a total of 56 Infantry Regiments.
Based on our 4/1 Jump ratio question this means 5 of which would be Jump Regiments. So less than 10% of all Infantry.
Half of the infantry regiments (28) are assigned as Single Regiments typically to garrison worlds, probably as a "liason" type position to coordinate with the planetary militia or as a core unit for the PM to form around & take direction from.
20 Regiments are assigned to the 4 RCTs.
This leaves us with 8 Regiments assigned as part of Infantry Brigades. So probably 2 Brigades of 4 Regiments each with an attached tank regiment taking it to 5 total regiments. I would guess that 1 extra Jump Regiment is part of one of the Brigades v/s being independently assigned as garrison.