I voted No, because while they are important to consider, I personally don't see them as being very predictive of an outcome in a battle.
And for most cases in FT, I find it pretty difficult to quantify each character's stats to begin with. Usually, character stats involve a lot of guesswork and subjective formulas because they are rarely explicitly stated in the manga.
On the rare occasion that the author does release character stats (via Tartaros character cards, for example), those numbers still seem somewhat arbitrary when compared to the actual battles themselves. However, I do believe that those stats can be a decent estimate when it comes to classifying the characters by tiers.
Anyways, when it comes to judging the outcome of a battle, I prefer to look at the situational or external factors involved in the particular match-up. For many fights in the FT manga, I actually think that the results of the battles could have gone either way, depending on the characters' individual performances at the time.
Sure, there are cases where stats become more obvious - in the case of higher-tier characters vs. lower-tier characters.
But if stats were extremely crucial in determining the outcome of a battle, then you would rarely see the characters try to outclass their opponents through the use of advantages/disadvantages.