I have read the investigation report (not in depth, it's a bit too turgid).
From the facts in the report, my view is that the captain was seriously negligent, although a 10 year jail sentence appears extreme. I don't have the competence to comment upon the flying ability displayed but the serious fault that, imo, amounted to gross negligence was the fact that he noted the anomaly in the fuel upload record but dismally failed to follow through.
Having identified the anomaly, the captain had several choices - he could have delayed departure until the 'missing' (in fact, non-existent) docket was found. Or he could have performed a 'drip-stick' measurement. If he had done either of these, the 'fuel remaining' misreading and incorrect FQI would have been identified. He also had a second (or third) opportunity to trap the original error (incorrect FQI) by performing the fuel used reconciliation at the intermediate stop (I'm not sure whether this is mandated or simply recommended/advised).
If I understand correctly, the reconciliation of previous fuel reading + fuel upload (as per the upload docket(s)) to current fuel reading is the first and last line of defence against an erroneous FQI indication. The entire purpose of that cross-check must be to trap errors and/or faults. As someone posted above, insufficient fuel is one of the few things that is will certainly result in an otherwise serviceable a/c making an early landing. In this case, the failure to apply unexceptional due diligence, on a matter that required no knowledge or training other than the ability to perform simple arithmetic, set at naught the inherently sound purpose and outcome of the cross-check procedure.
The captain's failure in this case is more serious and inexplicable because this was the first flight of the a/c after the FQI had been replaced; a fact that (I suppose) was noted in the technical log which the captain had (or should have) examined.
The other (to my mind) very serious fault that is mentioned but not given sufficiant prominence in the report is the absence in the procedure for replacing the FQI of a simple check to validate that the unit is functioning correctly. All that the manufacturer's procedure guide requres, it seems, is a visual confirmation that the LEDs on the unit illuminate. Well - that's no more than confirmation it has a power supply and is completely inadequate for validating its performance. How the hell is it possible for that procedure to be carried out without (at least) some 'sanity test' type of check that it is giving a more or less correct indication?
However, serious as that fault is, my view is that the captain's was more serious because his check was the last (and only) line of defence against a faulty FQI. Even the right FQI (new or not) could have been giving an erroneous reading.
In my job, I deal with financial calculations. I NEVER assume any calculation I perform is correct until I've done it at least twice and got the same answer each time. If I make a mistake, my employer may lose money (and so, as a result, may I), but nobody dies.