Sorry to keep piling on, and I realize things are still in beta, but I was messing around with the Export features just to see how well they worked. And here is what I found for each one (some I couldn't do, like MTGGoldfish, since I need to pay to import files):
Deckbox
When trying to import, I got an error on line 437 (in my file) which is:
1,0,"Kongming, \"Sleeping Dragon\"",Masters 25,0,Near Mint,English,foil,,,,,,,
It appears that it doesn't like the quotes for this card and won't import it like that. From what I can tell, based on exporting this card from their platform and then importing it again, you don't need to escape the quotes. You can just double them up. This line works fine:
1,0,"Kongming, ""Sleeping Dragon""",Masters 25,20,Near Mint,English,,,,,,,,
I then didn't get the error about cards but then it complained about the headers being wrong for some reason. It said it couldn't recognize "Count" has a header name. Which I think is more on their side than yours but if I copy everything but the header into a file exported from their system, it works fine. Just kind of weird.
Also, they have Theros as "Theros Beyond Death" rather than "Theros: Beyond Death" (notice the colon) that you export as. There were other set name issues but I didn't go through the rest.
Deckstats
The importer does not recognize the following sets:
MP2
GVL
DKM
Also, there seems to be a pretty major bug in that everything, including foils, use the nonfoil count. So, my Academy Rector was outputed as 6 nonfoils (correct) and 6 foils (incorrect). It should have been 1 foil. And anything without a nonfoil copy gets outputed with a count of 0, such as my Snuff Out and Haunted Crossroads. Which means about 3/4s of my collection didn't import at all.
Decked Builder
This one is kind of weird in that it requires the use of a CSV converter that they provide. This gets the CSV file into a Coll2 file. However, their format doesn't match yours. Yours uses these columns:
Total Qty,Reg Qty,Foil Qty,Card,Set,Mana Cost,Card Type,Color,Rarity,Mvid,Single Price,Single Foil Price,Total Price,Price Source,Notes
But their system appears to just look for these 4:
Set,Card,Regular,Foil
Which means I can't find a way to import your exported CSV into their site.
MTG Manager
It doesn't appear that there is even an import feature so I couldn't test it.
MTG Stocks
"Mystery Booster Retail Edition Foils" should be "Mystery Booster: Retail Exclusives".
All Judge promos should just be "Judge Promos"
"Secret Lair Promos" should be "Secret Lair Drop Series"
"Limited Edition Beta" should be "Beta Edition"
There were a bunch of other errors as well with sets, but I got tired of updating everything. Their import process makes me glad yours actually imports and then just spits out a list of "bad" records instead of making me correct everything on screen. It is tedious.
MTG Studio
The file export format appears to have the opposite issue of Decked Builder. In this case, your export only has 4 columns:
Name,Edition,Qty,Foil
But MTG Studio's import requires 7 columns:
Name,Set,Qty,Foil,Price,Condition,Notes
Pucatrade
For the most part, this worked pretty well. It did say it couldn't import the following but I didn't go into more detail as to why:
nullx Plains foil Near Mint English Theros: Beyond Death
nullx Island foil Near Mint English Theros: Beyond Death
nullx Swamp foil Near Mint English Theros: Beyond Death
nullx Mountain foil Near Mint English Theros: Beyond Death
nullx Forest foil Near Mint English Theros: Beyond Death
nullx Nightmare Moon foil Near Mint English Ponies: The Galloping
nullx Princess Twilight Sparkle foil Near Mint English Ponies: The Galloping
nullx Rarity foil Near Mint English Ponies: The Galloping
nullx Kenrith, the Returned King foil Near Mint English Throne of Eldraine
nullx Swamp foil Near Mint English War of the Spark
nullx Incubation foil Near Mint English Ravnica Allegiance
nullx Rakdos Guildgate foil Near Mint English Ravnica Allegiance
nullx Expansion foil Near Mint English Guilds of Ravnica
nullx Invert foil Near Mint English Guilds of Ravnica
nullx Dimir Guildgate foil Near Mint English Guilds of Ravnica
nullx Selesnya Guildgate foil Near Mint English Guilds of Ravnica
nullx Plains foil Near Mint English Dominaria
nullx Firesong and Sunspeaker foil Near Mint English Dominaria
nullx Kongming, \Sleeping Dragon\ foil Near Mint English Masters 25
nullx Beast in Show foil Near Mint English Unstable
nullx Secret Base foil Near Mint English Unstable
nullx Amateur Auteur foil Near Mint English Unstable
nullx \Rumors of My Death . . .\ foil Near Mint English Unstable
nullx Target Minotaur foil Near Mint English Unstable
nullx Island foil Near Mint English Hour of Devastation
nullx Swamp foil Near Mint English Hour of Devastation
nullx Dusk foil Near Mint English Amonkhet
nullx Commit foil Near Mint English Amonkhet
nullx Atraxa, Praetors' Voice foil Near Mint English Commander 2016
nullx Plains foil Near Mint English Kaladesh
nullx Island foil Near Mint English Kaladesh
nullx Mountain foil Near Mint English Kaladesh
nullx Forest foil Near Mint English Kaladesh
nullx Plains foil Near Mint English Shadows over Innistrad
nullx Island foil Near Mint English Shadows over Innistrad
nullx Wastes Near Mint English Oath of the Gatewatch
nullx Wastes foil Near Mint English Oath of the Gatewatch
nullx Swamp foil Near Mint English Battle for Zendikar
nullx Plains foil Near Mint English Magic Origins
nullx Turn foil Near Mint English Dragon's Maze
nullx Wear foil Near Mint English Dragon's Maze
nullx Swamp foil Near Mint English Return to Ravnica
nullx Plains foil Near Mint English Avacyn Restored
nullx Plains foil Near Mint English Ravnica: City of Guilds
nullx Island foil Near Mint English Ravnica: City of Guilds
nullx Mountain foil Near Mint English Ninth Edition
nullx Forest foil Near Mint English Onslaught
nullx Mountain foil Near Mint English Odyssey
nullx Forest foil Near Mint English Seventh Edition
nullx Island foil Near Mint English Seventh Edition
nullx Plains foil Near Mint English Seventh Edition
nullx Swamp foil Near Mint English Seventh Edition
nullx Plains foil Near Mint English Invasion
nullx Island foil Near Mint English Invasion
nullx Swamp foil Near Mint English Invasion
nullx Urza's Mine Near Mint English Antiquities
nullx Urza's Power Plant Near Mint English Antiquities
nullx Urza's Tower Near Mint English Antiquities
TCGPlayer
I couldn't figure out to import the collection.