Thank you for playing and writing some feedback! I really, really appreciate it.
This game follows the principle, that like in life, nothing is guaranteed.
So in this game, you won't ever be able to get 100% odds in the game, but you can crank it up to 99.999%.
You can think of the bonuses as additional sides to a dice. Like if a mission is 5/6 odds of success, a +6 bonus will give you 6 more sides to that dice. For 'extra-hard' missions, the odds are 1/(something) and you need to dig your way out from 1/6 to 5/6 before your bonuses count toward both sides of the equation.
... it is simple in practice - very hard to describe... I am hoping the percentages help players figure that out for them selves.
I do understand your logic behind odds, it is pretty much like missing a really crucial shot in games like XCOM even if it was 99%, it can happen because it could happen in the first place, and that is part of the fun.
In the case of this particular game, sure, a mission can fail even with all the odds in your favour because your role is just to send the right people with the right equipment, and expect the results on the next turn.
My critique is actually more about the lack of options to recruit new pilots or purchasing again the lost mechs, even if it is costly.
But then again, besides this point, I keep the same good opinion about the game.
Congratulations for your work