Regarding the narrow issue of adequate fuel and the means for ascertaining same:
Is it policy at TigerAir that the minimum required fuel may only be determined by the admittedly poorly trained company flight planning clerks?
As the pilot in command and the only person so designated surely the captain would be able to employ any means available (readin', writin', 'rethmetic) to decide if he had at least minimum fuel pre-flight? To suggest that the planning clerk is a better judge of that is depressing.
When faced with similar situations in the past I have opted for lots of extra fuel rather than wait for a new plan. So I tankered an extra couple of tonnes? The cost of that might run to $175, cheap to avoid a delay or other costly event.
That's what the initial episode amounts to: fail to (wrongly, as it turns out) seen to be prudent, and a couple of hundred bucks.