I will say with the nexus 7 and LineageOS I have had a recurring problem with USB OTG becoming unresponsive when using flash drives despite the service for charging and USB keyboard always works. No idea what it is and being a non-GNU Linux I am not sure how to track down the issue. the problem crops up and can persist for months sometimes if I am lucky fixing itself for a bit if I reflash to certain saves. The issue even presents itself in the TWRP recovery manager. Not sure if this a hardware or software issue but worth considering.
Of course this is a major problem because the MTP connection is super wonky.
Franky it is tricky getting data on and off of Android based devices, not sure if that is by design. But on the N900 be it a flash card, USB, USB host mode, wifi, or bluetooth the transfer is sweet and easy unlike Android.
(edit)
OK, today was hardware day...
I tweaked my slightly bent Nexus USB port, now it works, but it turns out that my little OTG adapter is NOT working . So not software or something inherent in the design of the Nexus, with the springy teeth the charge and keyboard cables/jacks worked fooling me.
I also got Amaze file manager going, it has an FTP server included. Cant get it working secure but for a few minutes of online at home annon login is enough to tweak or backup files from my laptop.
I bet the loose port is what was making my MTP connection so flaky too.
I will say that unlike the N900 the Nexus7's USB port is anchored down quite well and just took some bending with a screwdriver tip to get it OK.