£16k = £1,200 per month after tax. And you work 80 hours less per month for it.
I'm not playing 120 hours of poker a week. I'm playing 30 ish.

Your risk of ruin is obviously extremely high shortstacking 50NL with £450 behind, which strangely you seem to realise. "Going pro" is to start a career in your chosen field.... this is not starting a career, it's practically a novelty challenge.
Just to be clear, everyone is shortstacking. The max BI is 10bb, which just encourages people to go nuts. And I did emphasise the word "try". I'll decide if I really am pro at the end of the month when I analyse my performance and winrate.

Sounds like you're running really well too, but doesn't need saying that this is not a sample size worth discussing anything about at all
I feel like I'm running average, but that's a feeling rather than based on any actual analysis. But yes, sample size is obviously ludicrously small. I can only change that by playing.

As a long term venture, you can probably expect your winrate shortstacking 50NL to level out at about 1 BB/100
I think you are underestimating just how badly people are playing.

I'm not being an arsehole for the sake of being an arsehole,
You're not being an arsehole.

I think you're only using the term "going pro" because it sounds cool, and not because you actually are.
I'm being honest with my intentions. I want to make a living playing poker, and I think it's possible. So I'm completely sincere that I intend to "go pro".

You're taking a shot with a small bankroll in a high variance game to which you are adding extra variance by shortstacking.
See above about shortstacking. It's not a ratholing tactic that I am employing against full stackers. That would be a terrible strategy for going pro, so I can totally understand why you're all "wtf is this guy thinking?".