Ok, it seems 100% certain it's a non-MTK then. I'll make a kit to try force-flashing the regions using a microSD so get a CLEAN small card of no more than 32GB ready, formatted in FAT32. Other projects take precedence ATM so watch this thread in several hours from now.

EDIT: Butters had in fact made the required kit some time ago and posted in [Only registered and activated users can see links. ] here for ISG to use on a malfunctioning nuvi 1310 which he'd reported in Post #270 could not be flashed normally with Updater.exe. It was returning the same error you got (see his Post #272 also in this thread) and in his case the 1310 had indeed been wrongly flashed with fw for nuvi 12xx HWID 0971 (it was that same error screen you reported which had made me highly suspect your device may have been cross-flashed too). It his case the 1310 wasn't recoverable using software means and although in your case i'm now convinced the 1350 hasn't been cross-flashed, that's just unfortunately pointing to a higher possibility that it's had a hardware failure, simply because that can cause the exact same Updater error.

So to explain fully about this flash kit using Updater and a media card and why we need to try this method:

A device that is unable to get at least as far as displaying "Loading Maps" on the splash screen is unable to read a media card because it doesn't look for a card until after loading those essential files. Your device isn't loading files of course, and even though it can attain preboot that too occurs before the device looks for a card. However, the modified ramloader (aka boot.bin) in the RGN executed by Updater.exe forces the device to read an inserted media card much earlier, while it's in preboot mode. Provided the device's flash regions aren't physically damaged, then the two firmware BIN files on the card will be forcibly flashed to the appropriate regions (14 & 127) allowing it to boot normally. I note that you initially reported being able to reformat it using RMPrepUSB so the visible flash region in rgn 48 will be empty and that's ok because 1xxx devices are capable of booting when empty. Therefore it's not 'soft-bricked' by a corrupt file even if that's what did actually cause the original failure while in use. There should also be a copy made of it's rgn 41 (the non-volitile memory), and if a gupdate.gcd was present that is deleted - but as your file system is empty that command will fail which is of no consequence.

So download the file "SD Flash - Patched boot RGN.zip" from Post #286 and extract it to find a folder "Contents For Card" and two files, Updater.exe and 097201000630.rgn. Open the "Contents For Card" folder and copy the Garmin folder and 2 BIN files directly to the root of the clean small microSD then insert the card into the 1350 ensuring it's completely OFF. Drag the RGN onto Updater.exe to open it, put the device into preboot and start Updater. If the flash initiates properly it will take a while so let it run until it hopefully re-boots itself. Good luck.