To put this in perspective, if the Sentinel ranged damage scalar is somewhere around .80 to .85 as I *think* it is, that means it's only a little bit over a 25% difference between Blaster and Sentinel *base* damage. Of course, the Blaster inherent, build up and whatever else is going to dramatically inflate that for short periods of time, but Senintels also have a few tricks up their sleeves, and in particular these tricks all surround having more readily available and consistent damage- shorter cooldowns on their nukes, an extra high-ish damage single target attack...
As Sunsette alludes to later in this post, the reason why this is important is that differences as little as 10-20% can *radically* alter TTK in these older style RPG games where everything has a cooldown, and on sentinels in particular, their tweaks to push them towards more consistent, less spike-y damage paired with their use of armor sets means they get along with flat damage increases particularly well.
Aside from those specific points of notice, it's also because- especially in a game like CoH- It's far safer to increase base values in small slices, little boosts of 10% or 5% with testing in between. It's way, way safer for a game to make adjustments to numbers that exist at the bottom of a massive buff stack like this. Really, smaller increments in one direction are safer in general, as you're less likely to overshoot your target and have to start nerfing. If the player hemmoraging nerf patches this game experienced early in its life time taught us anything... It's that.