If we're realistic about our rebuild, the team is likely to be much better in 8 years than it is in 5 years. In 8 years, Larkin could be surrounded by prime Zadina, Hronek, Cholowski, Hughes, Lefreniere, Berggren, he could be going on deep playoff runs, he could have a cup, he could have a Smythe.. THAT'S when you don't want to negotiate, otherwise you end up paying a Toews (i.e. a Larkin) like he's an offensive superstar.
But all of this is speculation. Larkin could settle in as a 60 point player, no further improvement. The team could become a contender within 2-3 years and earn Larkin one of those massive contracts in 5 years. There are potential upsides and downsides to any contract term. I do find it somewhat odd that reactions to this contract makes it seem like 5 years is a short-term contract.
Personally I'm okay with not jumping at the gun to go as long-term as possible with Larkin right at this moment. Still a lot of unknowns about the future, and we will have lots more young players coming in, and if we notice that the team is improving and the rebuild is progressing fast; we can sign guys like Zadina/Rasmussen/etc to those 8-year deals and save money on them. You're never going to have 100% of the roster being underpaid. Some you will have to pay accordingly.