I know there has to be something that stops this archetype from being very useful but what is it?
--For a possession free spirit.
You have some reason to get into someplace secure. You find someone with access and you render them helpless and possess them, taking over their body and walking it into the secured location. The disguise and ID are not fake. Just walk right in.

I see some potential hangups.
-getting the right wage slave could be tricky. Using narcojet or stick and shock should be fairly easy.
-the target gets a resistance test even when subdued. If the resistance succeeds then it prevents another attempt for that day. It is a force*2 vs int*will test.
-preparing a wageslave as a living vessel gives a bonus to possessing them but it would take all week end for a skilled enchanter.
-Preparing a living vessel is permanent so the tampering with the wageslave is detectable, even if it is not inherently traceable.
-spirits or free spirits can not see or at least interpret "electronic projections", presumably that means reading electronic displays.
-viewing AR and VR is right out.
-passing through a ward can be cone with auramasking Masking and Extended Masking. The spirit uses its Edge in place of initiate grade.

--For materialization free spirit.
-getting the right wage slave or make sure they do not get in the way.
-asses the wage slaves aura in person or with a quicksilver photo.
-Hope you don't need to pass a biometric scan or enter a code on a touchscreen.
-passing through a ward can be cone with auramasking Masking and Extended Masking. The spirit uses its Edge in place of initiate grade.

I would allow the spirit to read what's on displays and computer screens while inside a body, they would use their hosts senses while in abody, not their own.

Ah yeah... I would say to that: Of course. Even materialized spirits should be able to identify symbols on screens and such. Animal spirits for example even get lowlight vision. One could assume materialized get normal sight.

Well, to the character itself:
While in low security it most certainly would work (Even though the spirit better learns as much as he can about his victim to impersonate him) it may be VERY hard to fool magical security. As long as you don't have masking (and a very high initiate rank/high roll on masking) you can be found out through a normal assensing. Also you still need to learn about procedures, telltale signs and passwords you need to know to pass through inspections. So you still need to interogate/mind control the victim before you posess him. Also having a good team to kidnap a victim and arrange it so you have time is still part of the run.

Other than that: Yes, a possesing spirit of high force and with a lot of initiations may be the best infiltrator possible.

don't know a real form metirsation sport could do better be an iocuors item and place you self in there pissesion. Then youlll be harder to find out plus you can learn codes procedures as well as getting in to where you need. Mic I'm some mind effcting spells to make sure you get worn picked up paddy security ect.

once your where you team needs turn to form X and bam do the run/part of run you need.