You're comparing mechs and tanks here not tanks and tanks.
An ERPPC is 7 tons of turret weight and 5 tons in the body so usually 13 tons total with 3 tons to spare in the turret. What's the alternative? You want something that does better than 5 point clusters, has no or a very short minimum range, and has similar range brackets, and doesn't jam or explode. That rules out all of the introtech energy weapons. It also rules out any autocannon 5 or less, any non-hvac autocannon bigger than 5, and any hvac at all.
So there's the ERLL, but it has a shortened long range bracket. It is a lot more efficient, but 20% smaller and the efficiency advantage evaporates if you try to mount more than one. There's the gauss rifle, which is great but is 15 tons base plus ammo and 1.5 tons of turret so minimum 17.5 and for a reasonable mounting 18.5-19.5 tons. That just doesn't fit in a 13 ton mass budget or alongside an SRM-6 in a 17 ton mass budget. There's the light gauss, but that is less efficient than the first ERPPC on a tank. Better range, but that means neither can be considered a substitute for the other. Nothing else has at least comparable range and better than 5 point damage clusters and doesn't explode when you look at it funny (I'm looking at you HVAC-10).
But off the ERPPC topic, the Manticore as it should have been:
Manticore Heavy Tank (Standard)
Mass: 50 tons
Movement Type: Tracked
Power Plant: 200 Fusion
Cruising Speed: 43.2 kph
Maximum Speed: 64.8 kph
Armor: Standard
Armament:
1 PPC
1 SRM 6
1 LRM 10
Manufacturer: Unknown
Primary Factory: Unknown
Communication System: Unknown
Targeting & Tracking System: Unknown
Introduction Year: 2575
Tech Rating/Availability: E/C-E-D-D
Cost: 1,944,250 C-bills
Type: Manticore Heavy Tank
Technology Base: Inner Sphere (Introductory)
Movement Type: Tracked
Tonnage: 50
Battle Value: 928
Equipment Mass
Internal Structure 5
Engine 200 Fusion 13
Cruising MP: 4
Flank MP: 6
Heat Sinks: 10 0
Control Equipment: 2.5
Power Amplifier: 0.0
Turret: 1.5
Armor Factor 176 11
Internal Armor
Structure Value
Front 5 42
R/L Side 5/5 33/33
Rear 5 26
Turret 5 42
Weapons
and Ammo Location Tonnage
SRM 6 Turret 3.0
PPC Turret 7.0
LRM 10 Turret 5.0
LRM 10 Ammo (12) Body 1.0
SRM 6 Ammo (15) Body 1.0
If you can't immediately see what was done to get it to fit in a light vehicle bay you probably weren't using it. It's not something easy to forget exact values for like armor or ammo. If you can tell, well you can decide if the exchange is worthwhile.
AND a Standard PPC is 7 tons.
wait, it isn't 7 tons plus five in the body?? nope. it's 7 tons, with the heat-sinks being integral to the engine, giving an 18 hex, ten point swat with no ammunition concerns (unlike, say, the 13 tons you'll pay to carry an autocannon). Mixed with the rest of the base model weaponry, that's a ten point whack plus crit-seeking from the LRM racks and potentially infernoes from the SRMs, making a well-rounded weapons fit on a chassis that can go hull-down, or sneak by with concealment and/or cover from L1 terrain.
While not as impressive as a battlemech of the same mass, it isn't
supposed to be-if you want to be impressive, you drive a 'mech. If you want to be highly effective and relatively cheap without breaking the bank? that's when you buy tanks, but 'highly effective' has a lot more to do, as they say, with what you do with it, than what it is.
The BEST upgrades stick pretty close to the original, 3026 layout, and leverage advantages in terms of mass (as your example above shows), refining the layout to be more uniform with the secondary weapons fit, adding movement or armor.
why? same reason as 'Sherman reasoning'-there were oodles of more powerful tanks out there, with bigger guns, heavier armor, whatever-but the U.S. could produce Shermans at prodigious rates, and they were 'good enough' as tanks (The T-34 also had this basic advantage over more advanced German and British designs.)
While hauling hedcappers IS nice, it's not
necessary, or even necessarily more useful than having reliable weapons that don't break your treasury to own and maintain.
That all said, I rather think that replacing the missile systems with a Multimissile launcher could improve the performance significantly on the basic Myrmidon chassis (Without needing an engine swap). WITH the engine swap, there's potential for an even broader application than the current model has, without wasting tonnage on heat sinks.
