Surely there's more 1st round picks who get a second chance at another club even without playing a single game at their original club
Than there are 3rd round picks who do the same
I don't know... first round picks tend to get at least a few games just based on the reputation that comes with being a first round pick in the first place.
Ignoring the 2020 draft as it's still very early, from the 2015-2019 period there are only three first round picks yet to play a game for the club that drafted them, let alone then being picked up by a second club. Ely Smith (Pick 21 2018, Brisbane), Jez McLennan (Pick 23 2018, Gold Coast), and Cooper Stephens (Pick 16 2019, Geelong). All three are still at their original clubs.
I'm pretty sure you have to go back to 2014 to find a player taken in the first round who never played a game for their original club, but then went to another club. Jarrod Pickett (Pick 4 2014, GWS) who was traded to Carlton in 2016.