Patrick Kane and Alex Ovechkin are the only wingers who have won the Stanley Cup in the cap era while having an arguable case to be considered their team's best player.
Kane had a top center in Toews on another line 2 of 3 Cups and a top 3 defenseman in Duncan Keith. Ovechkin had 2 number 1 centers.
There were way more teams that won the Cup whose best players were either clearly defensemen or clearly a center/defenseman combo without a top 5 winger. This includes Anaheim (Pronger/Niedermayer), Detroit (Lidstrom/Datsyuk/Zetterberg), Pittsburgh (Crosby/Malkin/Letang), Boston (Chara/Bergeron), Los Angeles (Kopitar/Doughty), and St. Louis (Pietrangelo/O'Reilly). The best winger among those teams listed at the time of their Cup(s)? 39 year old Selanne, Franzen, Kunitz, Lucic/Horton, Dustin Brown, 33 year old Marian Gaborik, Kessel/20- year old Guentzel, and Tarasenko.
Take it from a fan of a team who can only seem to build around 90 point wingers, finding a top 10, Right Handed defenseman is literally impossible and the teams that have them win a hell of a lot more consistently. All players have scoring streaks because offense is partly predicated on opportunity (a.k.a. luck). Playing good defense every day only requires excellent work ethic and hockey sense, if you have that you will be a great defensive player every game and consistency is what builds championship teams. Most players miss one or the other.
Jones is huge, with a big wingspan, and an excellent, arguably elite skater. That alone gives him a massive reach advantage because guys like him and Hedman take up half the zone (ANY zone) on their own with their length. His scoring comes and goes like all offensively talented guys (and especially defensemen) but he's a lock for 40+ points a year and can easily put up ~60 in a good year like a Hedman, Doughty, Chara or Pietrangelo to go along with their elite defense. Those guys are unicorns and basically ensure a real shot at the Cup every year for well built or balanced teams. And none of them are scoring like a Carlson or Karlsson or even a Rielly, because they don't need to in order to win every shift.
10/14 Cup winners in the Cap era had a top 10 defenseman or 2, and if we're extending to top 15 or 20 that rises to 12. Only 7 had a top 10 winger either as the centerpiece or as part of the core around other talented players at center or defense, and more importantly only 1 of those teams' best wingers made more than $7.5 million on the cap (Ovechkin 2018). That matters to me if I'm trying to build a winning team.
Marner is a great player. Jones is arguably just as good. Both are in the prime of their careers at their respective positions. One makes twice as much as the other while playing on average 7 less minutes a game. Teams have proven that you can win without an elite winger more consistently than without stud defensemen. Those factors are the kind of razor thin edge that pushes the defenseman over the winger in terms of leaguewide value. If Marner is worth a hypothetical 100% contract included, and he is, Jones is worth 105-110%. It's not a huge difference but all included I think most teams would choose Jones over Marner if they were to start from scratch with no other players to influence team need. No hyperbole, no exaggeration to prove a point, I just slightly prefer Jones for the above reasons.