I served with the CRAP / GCP of 2REP so I figure I am pretty qualified to give some history on the subject.
Pre-1990 the French Army consisted primarily of national servicemen led by a few regulars. This was the case in all regular French Army regiments including the 11 Choc, 1eme RPIMA and 13 RDP. In those days the French Army had very poor SF units with a large number of national servicemen who signed longer term engagements, but who were primarily conscripts. Although the regiments still existed there was poor training and almost all expertise had fallen away after Algeria.
In Gulf War 1 a call was made to France to provide a SF contingent; the French Army Command found themselves in an embarrassing situation having to deploy a CRAP (SF) unit consisting of conscript soldiers into the Gulf. Only 2REP CRAP were professionally trained SF. At that stage 2REP GCP unbeknown to the French Government were training as SF, their commanding NCO was former Rhodesian Intelligence and there were several former SAS, SBS and other NATO and Warsaw Pact specialists serving who could provide high level training. The GIGN also quietly trained with us.
What happened in GW1 was a disaster with regular army CRAP making stupid uneducated errors like picking up a BLU 97 sub-munition to ask what it was before blowing off his own head off and killing and wounding +20 others including several 2REP CRAP.
After GW1 the French Command had two problems with the REP providing it's SF; firstly it was embarrassing; secondly, they were foreigners and did not have the security clearances to be conducting the clandestine SF operations or be privy to sensitive intelligence. Up until Rwanda and Bosnia 2REP's CRAP unit which changed to GCP was very central to the COS; however, the COS was instructed to phase out 2REP from tier 1 as rapidly as possible. So in conclusion it is not because 2REP GCP are not trained or qualified to perform SF operations including Hostage Rescue that they are tier 2 COS; it is because consisting of foreigners they do not have the security clearance.
I agree with the comments that 2REP and the Legion are not SF, also that most legionnaires don't have what it takes intellectually to be SF However, isn't this true for all armies. The legion is a small army consisting of about 8000 engineers, cavalry, infantry and paras. Of the legion there is only one parachute regiment, 2REP consisting of about 1300 paras. Then there is the GCP consisting of 28 legionnaires. Imagine the previous experience the legion has to call on; ex soldiers from the worlds elite regiments, doctors, fighter pilots, lawyers, chartered accountants, computer programmers, micro mechanical and electrical engineers that join the legion for one reason or another and then become available to 2REP GCP. I haven't even touched on the 120 languages, where others send off soldiers to language school, the legion has native speakers. The Legion GCP is very capable, all that limits it is it's security clearance, and this is normal and I agree with the French Government.
The translation is 30 km full kit run in 2 hrs 29 minutes as part of a week of physical entry tests to SF Free Fall school in Pau France. 13 first places and 1 second place on SF courses, and record holder of Mont Louis Commando school "pistes vert et rouge" was a legionnaire of GCP. Not second rate by any account!