A pigment inkjet print NOT behind glass is superior---fade-wise---to Type C.
I don't get the 'behind glass' thing for photos; Paintings don't seem to need glass, why should photos? Exceptions perhaps for rare and un-reproduceable historic items.
Regular glass attenuates UV light a lot, reducing the print's exposure to it and generally slowing decay. However, I read that some print and inksets (R260 with glossy paper, R280) can change colour slightly faster behind UV filter than glass, as the blocking of UV changes the balance of wavelengths which the print is exposed to, leading to different rates of fading of the different inks, which then results in the color shift. However, this seems to be a relatively minor difference.
To ensure longevity it is probably best to study Wilhelm Research's results on fading on the same inks and paper that you're using, or choose materials which are tested to do well under the display conditions you're expecting from the print.
I've never seen fading of pigment-based Epson inkjet prints whether behind glass or not. However, the early dye-based inkjet prints were really terrible in terms of how they could shift colour in months in indoor light if exposed to ozone from an air purifier.
On the pigment-based Epson P700 and P900, this document gives print permanence ratings that show that the UV filter (glass) significantly improves longevity.
http://www.wilhelm-research.com/epson/WIR_Epson_SureColor_P700_and_P900_Printers_2021_07_23.pdfFor example, Epson Premium Luster Photo Paper (260)
displayed under glass: 135 years
with UV filter: >250 years
framed without glass or filter: 76 years
For these papers and inks, it would seem better to frame them with glass (and UV filter) than without any protective layer.
Also the dye-based Claria show better permanence under glass or filter:
With Epson R280 and Premium quality glossy paper:
under glass: 98 years
under uv filter: 82 years
displayed bare: 14 years (!)
14 years is shockingly bad IMO and such materials should be avoided. It's quite clear that the pigment-based prints show an advantage over dye-based.