Obstructing an unnecessary investigation is a big deal only because people fear-mongered us to believe it's a big deal.
Guy should get a good slap and a 6 figure fine. Not get his life taken away.
It's a bit more serious than that. It worked out to not harm anyone or do large-scale damages (fire, destruction, etc) this time, but it was still wildly dangerous and demonstrated a complete lack and disregard for aviation safety and rules.
A more apt comparison would be throwing a table off the Empire State Building, and it just so happened to not hit anything below.
I'm just saying, the "potential to cause harm" is vague here, it could be equivalent to throwing down a table off the Empire State Building according to careful physics calculations and precisely avoid killing anybody. It's still harmful (because the calculations can be incorrect), but less so.
(honestly had he not destroyed the evidence and made the plea that he constructed the crash in a way that was designed not to harm anyone, and it ended up not harming anyone, I suspect he might've gotten a lower sentence)