In Classic, hull bonuses would remain the same no matter what mark the unit was. A Missile Frigate would be 6x all the time.
In AIW2, they increase with mark. A Concussion Corvette would start at 6x, then increase to 7x, then 8x, etc. I wonder if this scaling should stay or not, as it means units with bonuses get better exponentially compared to those without.
First, a mention of the generic damage multiplier each unit gets with Mark, not the bonus damage ones. Only going up to Mark 5 here, but it gets worse at 6 and 7.
Mark 1: 1x
Mark 2: 2.1x
Mark 3: 3.2x
Mark 4: 4.3x
Mark 5: 6x
Now, a unit with a stat based damage bonus to armour (Autocannon Minipod) versus a unit (Vanguard) without.
Minipod:
Mark 1: Base 100 Damage, 2x Bonus Multiplier = 200 damage a shot.
Mark 2: Base 210 Damage, 2.5x Bonus Multiplier = 525 damage a shot.
Mark 3: Base 320 Damage, 3x Bonus Multiplier = 960 damage a shot.
Mark 4: Base 430 Damage, 3.5x Bonus Multiplier = 1505 damage a shot.
Mark 5: Base 600 Damage, 4x Bonus Multiplier = 2400 damage a shot.
Vanguard:
Mark 1: Base 240 Damage, 1x Bonus Multiplier = 240 damage a shot.
Mark 2: Base 504 Damage, 1x Bonus Multiplier = 504 damage a shot.
Mark 3: Base 768 Damage, 1x Bonus Multiplier = 768 damage a shot.
Mark 4: Base 1032 Damage, 1x Bonus Multiplier = 1032 damage a shot.
Mark 5: Base 1440 Damage, 1x Bonus Multiplier = 1440 damage a shot.
So at Mark 5, the Minipod has 12x the damage, while the Vanguard only has 6x.
Of course the Minipod only gets that much because it's shooting at a preferred target. With the stat system however, you could simply take Concussion and Pike Corvettes, units which get a bonus against low and high armour respectively, tech them up and somewhat stomp everything, as has...happened, a lot before.
In addition, being able to research Mark 5, 6 and 7 normally combines with the above exponential scaling to make monsters of a unit. It also means you don't need much unit diversity: If I already have Pike Corvettes, why would I get Minipods? It's better to just keep upgrading what I already have. Why get those Raiders or Vanguards, if they give less return on the science I pay, because they have no damage bonus scaling?
(It's incidentally weird that you can get better tech units than the AI, and have a single unit type powerful enough to stomp super units. I have no idea how Fallen Spire would work with this, or the units unlocked from controlling Fabricators).
I will note that Classic did have some units that did this. Paralyzers would have longer durations, Spiders would do more engine damage, etc. However, these might be excused, as they were not really meant for damage, and thus wouldn't gain much from the normal scaling, so they must gain it elsewhere, in their effects. They currently do this in AIW2 as well, mostly.
This is just a curiosity right now, something I've thought about a few times. Won't be doing anything on it.
Hope I've explained it okay. Please poke the necessary holes in the logic, thanks!