Do you not understand the premise of team control and why teams like to get more than the bare minimum number of years out of a drafted player?
A player who hits UFA (generally the first time a contract expires after they reach age 27*) gets big money because he’s able to take the highest bid he’s offered - and the highest bid, the most desperate team, usually pays a LOT.
A restricted free agent (generally, under 27*) is largely limited to negotiating with their rights holding team** and doesn’t really have the leverage for big money.
A team usually likes to sign a player for years beyond the first summer he could become an unrestricted free agent. To give up the open market payday, the player demands to be paid something somewhat close to what he would get paid on the ufa market for those years.
So yeah, if he signed a 7 or 8 year deal it would have been in that 8+ million dolllar range, but Carolina would have secured him for many many years beyond that earliest-ufa year (26-27). And assuredly whatever contract he signs next will be 8mil, 9mil or higher. But now that contract is unlikely to be one that keeps him in Carolina.
They got him cheap and short term, because they couldn’t agree on long term. But that’s not a win for them, for a top forward to walk at age 27.
* 27 or 7 years of nhl service, whichever comes first. For Necas it’ll be 27 (which will probably also be after his seventh year)
** restricted free agents technically can be signed by other teams to an offer sheet, but it’s a practice so painful (the incumbent team can match, and if they don’t the signing team has to give substantial draft pick compensation) it’s seldom attempted and even more seldom successful, and not really much of a factor in rfa contract numbers.