No weapons (that I can see) have a damage type listed. What damage types are everything? (relevant for bypassing DR)
1. Echoing.
2. Also as is there is no point in using Minimization. Perhaps Great Agility/Targeting should be adjusted to provide extra bonuses if you focus on being smaller. Arsenal also appears unaffected by changing you mech size, maybe in a way this avoids penalizing Miniaturization but then again Built-Ins are which forces the smaller mechs to use Arsenal which inevitably forces all small Mechs to rely on melee (see below) where they will auto-fail opposing Grapple Checks which presumably disables use of their Arsenal and rely on their inferior Built-Ins for one sided battles.
3. A more in depth look at DPR.
Using Gargantuan, 30 Str/Dex, for the opposing DR without Arsenal you can reach 35 so let's go with that.
A) A Greatsword deals 24d6+10 (94 avg), it costs 6,400gp but while Enhancement costs don't rescale making a Masterwork version costs 44,800 so let's just stick to that normal figure. Assuming three attacks per round because maybe you're looking at taking lv14 that's 118 after DR.
B) Focusing on Mech weapons, you can take Mightyx8, Pairedx1, & Rending. This gives you a double 4d8+26 (44 avg) per attack action, or 156 post DR after six attacks. More attacks, more damage, but costs several upgrade points.
C) For Heavy let's look at the Antiship Beam Sword which is one of the most powerful weapons and as lv3 can be Linked and assuming Mightyx8, you get two attacks of 9d12+36 (94.5) for 119 which comes out pretty close to the cheap Greatsword but has Power/Concussive/Disarming making it a better choice unless you need to trade those Mech properties away for gear-related Arsenal.
Seems fair right? Well let's look at Ranged. A +10 Longbow costs 140,800gp so instead let's just go with a Heavy Repeater for 16d8 (72 avg) which is three attacks and 111 after DR. Built-Ins via Tank become 3d8+26 (39.5 avg) or 129 after DR. And for Arsenal we have two choices, Linked lv3 comes to 3d6+26 (36.5 avg) or
9 after DR and none-Linked comes to 4d6+26 (40 avg) or
15 post DR. Even moving back to a Heavy Railgun for 12d10+36 (102 avg) even after post Rending DR that's only 84. Ranged Arsenal just isn't worth using.
4. Minor nitpick but your Arsenal dice are all over the place with no discernible pattern beyond Ranged gets about an average of 1d6 per level. Like lets look at melee, both heavy & not.
Lv1: 1d8 (4.5) / 2d10 (11)
Lv2: 2d6 (7, +2.5 gain) / 9d8 (40.5, +29.5 gain)
Lv3: 2d6 (7, +0 gain) / 9d12 (58.5, +18 gain)
Lv4: 3d6 (10.5, +3.5 gain) / 12d12 (78, +19.5 gain)
Lv5: 4d6 (14, +3.5 gain) / 20d10 (110, +32 gain)
Lv6: 8d8 (36, +22 gain) / 19d12 (123.5, +13.5 gain)
Lv7: 10d10 (55, +19 gain) / 30d12 (195, +71.5 gain)Which is probably why Heavy melee's figures can keep up with the other choices.
6. btw, given the "future" nature of a Super Robot campaign how does this interact with the DMG's modern weapons such as a Shotgun or d20's weapons, since you have rail guns & colossal mechs, say a Pulse Rifle?