As far as I can tell, the D&D Next Fighter has the best (or among the best): hit points, armor, durability, attack bonus and melee damage.
Adding in advantage to all saves seems a little much.
Worst in: spells. And that makes all the difference (still).
I am not sure it would be too much, because I agree that spells make all the difference.
I don't care that much about balance (unless there is something really glaring), I just want to play a game when choosing
any character feels rewarding, and if I choose to play a Fighter it's because I feel like in this adventure/campaign
I want to fight. That means, most of the times I'll be the first to go to the front line to attack a monster, and the last one to retreat when things go badly. If I had the best saving throws of all, in addition to the other stuff, I will just do those things with more confidence. (It's not the only way to play a Fighter for sure, but it's still a major one)
Now on the other hand, when I choose to play another character (i.e. 90% of the times), I probably feel like focusing on something else, which most of the times doesn't imply recklessly jumping to the front line. I don't need the best saving throws, and I am
not bothered if the Fighter gets them. It just means that I have a better chance at... not having to be in the front line.
I can understand that for "balance" it may seem to much, and I am confident they'll remove this ability after feedback. But for me it's not, for me it actually sounds like a good idea to make the Fighter "more Fighter".
Actually I've said a few times in the past that I'd be fine even if the Fighter had
twice everybody else's damage output in combat. That's
not the balance I care for. Instead, the balance I really care for, is that all character classes are equally rewarding to play, across the whole game (and not equally in each pillar). If I think too much about who gets the best bits here and worst bits there, it becomes a competition between PCs... then looking at your friend's better ST or higher damage/round will make me feel less rewarded because I'm trying to measure reward against the same purposes of playing a class i.e. deal damage and stay alive. It's ok once in a while to play a campaign like that, but on the long term, I'm just not interested in this kind of game. And that's one of the main reason I skipped 4e btw, where everyone too similar because "crunch balance" is paramount.