Both flywheel HP and road wheel HP are important, but in different ways. There are a few factors that can give variance in readouts on a road wheel dyno from day to day, and tolerance in the dynos. But drivetrain setup can also really affect your numbers. If Jai were to put his engine on top of a weak old drivetrain, he'd get better numbers than putting it on a stronger drivetrain (like the one I'd imagine he has). It might look more impressive, but anyone with their head screwed on correctly will realize that the person just wants a number, not a real, reliable car.
A strong road diff or a competition diff would have to drain more power than a stock one. I don't know the differences between drivetrains with Minis, but I know that a lot of people reckon that changing from a stock diff to a 9" diff ruins your dyno readouts - driveline losses go from 25% to more like 40+%. So while two blokes may have an engine which makes 300rwhp, if one has a stock diff he's only really got about 400hp at the crank, where the bloke with the 9" has more like 500hp. And his setup will last a lot longer. Mr 400hp will have credit at the pub, but Mr 500hp has a better engine and will enjoy better reliability from his diff. And he'd be the one who you'd listen to when he's giving engine building tips.
Besides that, all the figures you see in magazines and published documents are all flywheel numbers. The old quotes of 30hp for an 850, 44 for a 1098, 55 for a 997/998 Cooper, 63 for an MPI, 75 for a 1275 S, they're all flywheel figures. If you factor in that Jai's got at least 20% (if not more like 30%) drivetrain losses, that puts his number at more like 125-150hp.

Which compares well with a 4EFTE at 130bhp stock or a G13B at 100bhp stock -
both at the flywheel. Something to think about for those considering conversions. To my mind, numbers like that mean a conversion only really makes sense if you're after a 5 speed gearbox.

Or absolutely insane, impossible to control power - go for it if that's what you're after!
Further yet, many ricers out there only know published figures.

They forget or don't realize that, yes, their WRX has 155-168KW stock, but it's actually got less than 120KW at the treads...
And the number appears! 140-odd hp - so better than double what it started out with. More than 100bhp/litre. With a single carb and (I presume) a 5 port head. Any number like that is a real credit to the owner and builder. Well done!
