After looking at this, my main conclusion was that going from iterative attacks to a single attacks with flat damage increase are not even close to being the same. Also, adding a flat damage bonus is not linearly "balanced" across the range of attack rolls.
Let me explain.
I listed the % increase and delta values to show "theoretical" and in-game data. % increase in damage is nice from an analytical point of view but doesn't do much to show what's going to happen at the table.
For example, regardless of the average damage done, the % increase is always the same. My Excel chart uses average damage as a variable so the table repopulates as I change it. Whether your average damage is 1 or 50, going from 1 attack to 4 attacks is a 25% increase in damage.
However, the delta of going from 10 to 25 ave damage for 4 attacks is 28.5 to 71.25. That's a huge difference at the table, but percent increase doesn't really show you that.
Also, as the roll you need to hit goes up, the delta goes down dramatically, even though the percent increase can be fairly high. That means that as you hit less, the value of extra attacks goes down. You might have a huge percent increase in damage from a single attack but if your average damage is low to begin with because you don't hit very often with a single attack, you are going to have even less chance to hit with iterative attacks.
So how does this compare to a static damage bonus with a single attacks? The most obvious is that it penalizes characters with a high AC. If a character needs to roll very high with their first attack to hit, iterative attacks won't be boosting their average damage very much. Now however, that player has a flat damage boost for when they do hit. The player with the high AC will now take more damage on average.
Also, I think it will make high-level play less deadly. Attack bonuses scale a lot faster than defense/AC does in d20. That's not by accident. With only a single attack, even with a +10 bonus at level 20 (Saga grants a +1/2 level bonus), players will be donig a LOT less damage at high levels, which will potentially make combats much longer. Maybe this was a design goal, I don't know.
This may also have interesting implications with their damage track system. I don't yet know how the Threshold is calculated (in the previews, a level 1 character had a threshold of 14 while a level 8 character had a 22), but depending how it scales, with a flat damage bonus, it seems like there will be a greater chance to eclipse this threshold as the damage bonus increases.