First off, I don't think you are doing anything wrong. It can be hard to get things adjusted just right so that your Mr. Moonie can start doing better. Getting little to no support from the vet is all too common. You can get some good suggestions here on the board. You can also fire that vet and find one that will work with you.
Now, you probably know this already, but let's double check. It's great that you are feeding some small meals during the day and night. Are you making sure you take any leftover food away 2 hours before you do his BGL test? Are you testing his blood sugar, then feeding, then giving insulin?
You are doing great with the home testing. When your schedule allows, more consistent mid-cycle tests would be very helpful. Even if the day ones are just on your days off, and the night ones you have to set an alarm for. A few days with a +5 and +7 reading would be awesome. A curve test would also help. That's when you pick a day and test every 2-3 hours for 12 hours. Seeing that curve can really help us see what's going on.
It is always possible that Mr. Moonie needs a slightly higher dose. Every Cat is Different. You should let a member familiar with Lantus advise you in that, though. Lantus is very different from what I use with my kitty. But try not to fret. Yes, it's very frustrating not to see progress yet, but he will get there. It often takes a bit of trial and error to find out what works for your cat.