Paddack's extension can be a starting point for thinking, but the two pitchers' contract situations are very different. Paddack still had two arbitration years ahead of him, so he had less leverage when considering whether to accept the team's offer to guarantee him some money. Mahle is already eligible for free agency after this season.
Look at it a different way. Before signing his extension, Paddack had earned about $5M in major league salary*, which is good money but not quite at the "set for life" level for a variety of reasons. The Twins' offer did take him past that threshold. By contrast, Mahle has earned above $15M to date. Assuming he's invested wisely, the Twins can't really approach him and his agent with "we'll guarantee you life-changing money" because his life is already changed for the better.
Paddack chose not to gamble on a far higher payday at some intermediate point, during which something unrelated might also go wrong, while still maintaining the potential for a good outcome in free agency further down the road. Mahle might see the gamble as less dependent on anything besides recovery from the elbow surgery, and he's better placed to shoulder** the risk if he wants to roll the dice. Paddack thereby assured his own financial future; for all I know Mahle might be trying to fund a charitable foundation next, for example.
I think signing Mahle's going to be harder, because from the Twins' perspective the two situations are indeed pretty similar. The team will have to risk more, with more or less the same potential reward.
* I'm taking my numbers from b-r.com, which I find sometimes to be unreliable for the kind of analysis I want to do.
** No pun intended, but there it is.