My issue with such drastic hullmods is that they force you to use certain weapons.
That is actually my point. is there another ship in the game that actually does well with Gravitons as party of it's primary armament as opposed to an afterthought support weapon?
Midline already has the Falcon and the Champion. Falcon is capable of using said Heavy Blaster and Ion Pulsers because of it's speed. Or an Ion beam if it wants. Or a Phase lance. Champion is medium speed with energy and ballistic mixture, along with missiles so it can actually effectively kill stuff.
Eagle is always going to be stepping on some other ships toes no matter which direction it goes. If we make it faster, its stepping on the Falcon. If we give it a large mount its moving closer to the Champion.
A medium mount beam specialization would be giving something unique to midline and to the game overall. Or at least, I can't see the Eagle stepping on any other ships specialization in that direction.
You ideally want to have a situation where giving up something has an actual payoff. For example that hullmod would make sense on a very speedy ship that can just use projectiles easily. Here I'd just continue using Phase Lances and Gravitons. Doesn't change the ship in any way except making it more punishing when deviating from the "intended" build, and sure more damage.
I'm looking at it from the fleet and overall game perspective as opposed to the individual ship perspective. What you're giving up is the large missile mount of the Champion or the speed of the Falcon. It's at the ship choice level instead of the fitting level. The whole point is to have a ship that does in fact want to use Gravitons, unlike nearly every other ship in the game. The Eagle loses some flexibility in what is optimal for it, but the game as a whole gains something new.
Right now, as far as I know, the in development Eagle is going to be providing 30% more damage per DP spent. You could also imagine that beam built Eagles have perhaps, 25-30% of its damage coming from beams. The ballistics certainly are the lion's share of long range damage output, simply because it is hard flux. So if you double that 25-30%, then that is similar the 30% per DP gain we are expecting by dropping to 17 DP. So such a beam boosted Eagle might be worth 20 or 21 DP.
This is also why I feel forced to use Heavy Blasters and Ion Pulsers on high tech ships without large mounts.
Which is saying no ships really use said weapons. Which by forcing the Eagle into favoring said weapons, means you might have an actual reason to use said weapons on at least one ship in the game. If you want a ballistic + energy projectile midline ship, the Falcon and Champion both exist. Or if you explicitly just want Heavy Blasters and Ion Pulsers, the Fury, Aurora, Medusa, Hyperion all exist. At least this way, the game gains something it doesn't have yet. A cruiser that you might actually want to fit beams to instead of Heavy Blasters and Ion Pulsers.