Exactly. Quite frankly, the success rate for teams making big additions at the deadline is quite low. Teams that make the big swings at the deadline very rarely win the Cup that spring. Even the years Tampa made significant moves, it's not like they went out and made a bunch of big swing acquisitions - they just overpaid for role players, sacrificing a lot of draft capital in the process. In fact, they made their biggest swings the year they lost in the finals. The year they used Kucherov on LTIR to massively exceed the cap, their big adds were a broken Gaborik (for LTIR space) and David Savard. The way they really took advantage of it was in the offseason leading into 20-21, keeping their key pieces and better role players on the roster instead of being cap casualties.
On a cheap deal, it certainly would be worth the experiment. Worst case scenario, he gets a run of games, doesn't look great and becomes depth or retires. Best case, he's the solution for the #3 C slot (I don't think he's capable of more than that anymore - even before he took time off, his play was starting to drop off).
Allegedly, his play dropped off because he was "suffering from Chronic Inflammatory Response Disorder” that appears to have been resolved (see below). As we've seen when guys come back after a hold out, it often takes them quite some time to recover their game (ie Nylander after his hold out for a few months experienced a 33% ppg drop off for the balance of that season). In Toews case, he's 14 years older than 22 yr old Nylander was, so he probably won't be able to bounce back after 2 years off like Nylander couldn't when he 22 years old missing a few months. But he won't have to reach the top 6 level Nylander did as Toews would be in the bottom 6.