Over the last 3 seasons, Marner has had a 21% drop. Over the same time period, Tkachuk has had a 20% drop. Is Tkachuk a "soft little brat who gets outmuscled and turns into a mediocre player come playoff time"? Surely he will never win a cup, right?
2013-2017, Crosby had a 23% drop. Is Crosby a "soft little brat who gets outmuscled and turns into a mediocre player come playoff time"? Surely he will never win a cup (let alone two within that timeframe), right?
In the 2020s, Stone has had a 27% drop. Surely he will never win a cup, right?
2018-2023, Stamkos had a 32% drop. Surely he will never win a cup, right?
Over his career, Marner has a smaller drop off than Matthews and Tavares on his own team. Why are you going after Marner instead of them? Less of a drop than a bunch of players around the league. I guess Panarin, Meier, Kaprizov, Stamkos, Robertson, Petersson, Connor, etc., etc. suck.
You're actually hurting your own argument with this, as it makes it pretty easy to see how situation-based playoff production is, and how silly it can be to compare across teams experiencing vastly different things, with no context. In the situation Marner has been trying to produce in, those players put up 33 and 41 point paces. They moved to teams experiencing easier situations to produce, and instantly started producing more. What a coincidence! Marner's production changes align with the team's production changes, which align with the production changes of the teams and players that face the opponents and goalies that we face after us. What a bunch more coincidences!
I'm not looking to pay him 15m, but there's absolutely nothing wrong with the 12m you mentioned earlier, or even higher. We've had ~20m cap space in each of the last two offseasons. Cap space is not the magic fix-all that some treat it as. There's really no realistic alternative(s) that is worth spending it on more than Marner.