Okay so lets see what the texts says:
SPIRIT AND INTENTION
After a Mark or Free Kick has been awarded to a Player, a Fifty Metre Penalty will be awarded against the opposing Team which delays or impedes the play, or behaves in an unsportsmanlike manner.
Okay, did Sheerin delay or impede play? Nope. (Did Cotch? Nope, the ump literally hadn't made it clear what the decision was so it was impossible to have delayed play)
Did she behave in an unsportsmanlike manner? Nope. (Did Cotch - heaps of times, but not that time.)
There is no question that an ump CAN award a 50 for not giving the ball back. The reason people don't like the decision is because the umps are supposed to govern by BOTH the SPIRIT and the INTENTION. There is no way to interpret Sheerin's act as an attempt to hold up play. None. (And in my opinion the same applies to 2019 example.)
I have some empathy for this logic. We would need to get an umpire to advise if they are allowed to overrule a specific rule based on spirit and intent in general play and before the final siren. We do have the ‘common sense’ logic that got pulled out this year against us when the ball wasn’t returned to our player after the siren and 50m wasn’t awarded. However, It also depends how you interpret impede - I’m pretty sure wasting time is considered impeding so yes time was wasted and the play was impeded because the ball wasn’t returned to the correct player. After the siren you can’t waste time as the clock has run out.
With that said you didn’t post everything which is a bit disingenuous.
19.2 WHEN IMPOSED
Where a field Umpire has awarded a Mark or Free Kick to a Player, or a Player is preparing to bring or bringing the football back into play after a Behind is scored, a Fifty Metre Penalty in favour of that Player will be awarded if the field Umpire is of the opinion that any Player or Official from the opposing Team:
(a) has moved off The Mark;
(b) when in the immediate contest, unreasonably holds a Player after that Player has Marked the football or been awarded a Free Kick;
(c) when not in the immediate contest, holds a Player after that Player has Marked the football or been awarded a Free Kick;
(d) enters or does not make every endeavour to immediately vacate the Protected Area, except when the Player is accompanying or following within two metres of their opponent;
(e) has not returned the football directly and on the full to the Player awarded the Mark or Free Kick;
(f) engages in any conduct which delays or impedes the play; or
(g) engages in any other conduct for which a Free Kick would ordinarily be awarded.
19.2.e is pretty clear so I still think it’s dumb as a player if you rely on anything other than that rule as it is written in what you chose to do.
Separately I’m all for any efforts to stamp out gamesmanship (gameswomanship?).