Not at all negative, this kind of stuff is always appreciated! For what it's worth, the chance of rolling a 6 or lower on 2d6 is 41.66%, so the baseline odds are slightly in the PC's favor.
This game takes a lot of inspiration from older games where the risk of failure was pretty high - say, you have to roll a 15+ on a d20 to pass a difficulty check - so a lot of the time, the most successful missions are ones where characters avoid rolling the dice as much as they can. This might mean staying out of combat, talking their way out of things with pure RP, setting up several boons to give themselves advantage when they do have to roll, etc.
Having characters be disposable, constantly die for pointless reasons, and only become a person you're willing to get attached to when they've stuck around for a few missions is 100% intentional - you're disposable soldiers, and the ones who are either strong or lucky enough to stick around will be the characters you end up fleshing out. That isn't to say I haven't seen several characters who players really got into before deploying then and managed to keep alive—it just helps to play starting level characters as though you were really there, and getting shot once or leaving one thing to chance could really, actually kill you. Also, I'd see if your players are interested in the pamphlet adventure we put out called HAZARD FUNCTION—it's a sort of microcosm of this idea where you play three Very weak characters at once and whoever makes it out alive graduates to being your "real" character.
That said, adding a floating +1 is a somewhat common house rule I've seen for the game. Giving out some extra WAR DICE, using the Chopper Chatter rule, or just encouraging players to choose them as rewards can also help with this; we added the mechanic so people who are having a string of bad rolls can push a check result up when it really counts!