We know with reasonable certainty that Carlsen is the stronger player, thanks to the rating system. Championship match has always be about more than being _just_ the stronger player.
Because the number of games played was too short, the game score wasn't allowed to reflect the true strength of the players.
Being able to perform "on the day" is an integral part of every sport championship and the thing that makes them exciting.
(I suspect no violation of the FIDE laws of chess, which concern themselves primarily with the conduct and outcome of individual games and have little to say on the deciding of matches).
Note also that computer evaluations of the strength of a position do not necessarily reflect the ability of a human being to play it. Not merely due to move depth and complexity (like when Stockfish comes back with a hilarious "mate in 24"), but also time: I recall moments in Carlsen vs Karjakin where the engines judged SK to hold a positional advantage despite mere seconds remaining on the clock.
Karjakin had a winning position in game 9, but did not find the key move Qc4. He analyzed this line, but did not see Bg8 and thought it's not winning.
Yasser Seirawan had an interesting suggestion. Make championship matches 13 games, not 12, with the challenger getting white 7 times and the defending champion getting white 6 times, and with the championing retaining the title in the case of a 6.5 - 6.5 tie.
One nice thing about Seirawan's suggestion is that it does not involve rapid or blitz. Many people don't like the idea that the world championship of classical chess might be decided by rapid or blitz games. (There are separate championships for rapid and blitz, held annually).
As computers get better and better at chess, I wonder if it might become reasonable someday to use computer evaluations to break ties? There has been work on using computer evaluations to measure how accurate and strong chess players are. Computer scientist and IM Ken Regan has done a lot in this area, both in the context of trying to determine how strong past players actually were, and in the context of trying to determine when someone is using a computer to cheat.
For instance, in this match Carlsen had winning positions in some of the drawn games, but was not able to convert. I don't think that in any of the drawn games Karjakin ever had a winning position. I suspect that if polled, most GMs would say that Carlsen outplayed Karjakin during the classical portion of the match. With computers, that could be put on an objective basis.
Svidler is an interesting commentator. He has a quick and sharp wit. During one of the earlier games, when Eric Hansen was co-commentator [1], they were talking about IM Lawrence Trent (Fabiano Caruana's manager). I didn't catch all of it as I was listening while working, but apparently Carlsen was playing an opening line or something that Trent doesn't think is good. Hansen said something like "I wouldn't want to be Lawrence Trent, betting against Magnus Carlsen". Svidler immediately shot back, "That sentence was too long".
[1] This was on chess24.com. Svidler and Hansen were commenting for them, not for the official broadcast. For the later part of the match, the chess24 commentary was Svidler and German GM Jan Gustafsson. Both the Svidler/Hansen and the Svidler/Gustafsson pairings were quite good.