Suijin said:
Technically size modifiers only apply to ranged combat not melee. The size description says "Size is an important factor when shooting ranged weapons", and also the to-hit penalty/bonus chart specifically mentions the +10 bonus as "shooting a Hulking target".
Also the modifier to-hit a horde specifically says to treat it like an individual and also only refers to it as a size modifier (which should mean RAW the size modifier only applies to ranged combat also for hordes).
You do get bonuses for outnumbering an opponent in melee, you also get a ton of different bonuses to ranged combat, point blank, size, red dot sight, etc.
For the exceptional and master weapons you have to spend exp for the signature wargear or spend requisition to get them. Meanwhile the ranged combat guy can spend either the exp or requisition to increase his to-hit or damage also. You aren't really coming out ahead of ranged that way.
If you go balanced weapons then you are giving up damage from having a powerfist, etc. You can get a shield though, but so can a ranged person actually.
You can't dodge or parry a horde in melee, but you can dodge a horde at range.
You do have some safety from ranged in melee I admit, and you also don't run out of ammo. Two big benefits.
If you read it like that, and only apply size modifiers to shooting, you are definitely shafting the melee guy. But, although the Size heading does have the line about shooting, it does not say they do not apply to melee. The bonus/penalty chart with the +10 bonus is an example, not an exclusion. It does say 'Attacking' in other examples, but if you restrict size modifiers to shooting only, then yes, you might as well tell your Assault marines to pack up and go home.
Why would it be easier to shoot a Enormous Hive Tyrant from 100m than hit it with a sword? The fact that it's bigger should make it easier for both options.
For hordes, melee should get the bonus as well. If there are so many combatants that you can't dodge their attacks, there are enough opponents that you would be hard pressed to miss them with every swing.
And one comment on your power fist comment, while not balanced, lightning claws allow a parry and, depending on do 1d10-(6- unaugmented SB) less damage before adding the +1 damage per DoS and is Tearing. The fist wins for Max damage, but the claw is really close and has a higher RF chance with Flesh Render.