If you swap Liam Martin and Luke Garner, Garner is probably playing origin instead of Martin.
Neither are world beaters, but Martin has had the luxury of playing with the likes of Cleary and Luai while Garner has spent his entire career in first grade tethered to Brooks. Arguably the best situation in the league vs. worst situation. Boggles the mind that Martin wasn't dropped for origin 2 (or even picked in the first place) but just serves as evidence that a player's abilities, or perhaps even just the perception of their abilities, are so greatly influenced by where they play and who they play with.
He's also been coached extremely poorly. He's a centre/second-rower hybrid who runs good lines and had the pace to get on the outside of his defender and help create overlaps. He looked quite good as a line runner for when playing outside Benji, then ineffective with Brooks. Though you probably couldn't find a bigger disparity between one of the best ball-playing halves the game has ever seen in Benj and Brooks, who's a miserable ball player (probably being generous).
Rather than attributing Garner's lack of effectiveness to who he's playing with, Madge decided that Garner's problem was he was too small. So what happens? You ruin a player's strength, turn him into something he's not and surprise surprise, he struggles. Article below for reference:
Wests Tigers training and conditioning staff have told forward Luke Garner to eat anything he wants because he has to put some weight on.
www.nrl.com
Garner's come back this season looking like he was pre-2020 and no surprise he played pretty well when filling in at centre and has looked the best he has for a couple seasons.
I wouldn't be surprised if he has a good run at Penrith at all. By no means is he a great or complete player, but he's good some useful attributes and a coach and system that will get the best out of him. Plus they've managed to sign him at a time where his value is at it's absolute lowest. Meanwhile some team like us/Newcastle/St George will sign Liam Martin for 2-3x what Garner is on, and be stuck with a marginal improvement but a huge hit to the cap.