This was always the issue. Most people didn't question the Tavares signing at the time, but many people did voice some concerns about whether they really needed him, and the issues with the cap going forward. Those concerns, which mostly looked at the later years of the contract, were dismissed. The issues with the signing started to sprout right away, though, such as needing to trade Marleau for a 1st rounder.
This is a lesson for all teams. Ottawa didn't learn their lesson, and neither did the media, when the Sens signed all those vet forwards. Everyone proclaimed that the summer of Dorion, and it has been a disaster.
Team construction is the most important thing in hockey. You don't take/sign a huge contract just for the sake of it. This isn't like the draft where BPA should rule all.