it doesn't matter that you can tweak and torture mechs with the build rules in CBT, what does matter is that LBX10 was considered not good enough and thus was changed.
All I was saying is the Thor Prime wasn't tortured much. 1 DHS and 1 ton of ammo in exchange for a 2 tons heavier weapon. But it's not a free buff as you seem to imply; what would you sacrifice to upgrade the Thanny Prime's weaponry?
If the Mechlab is completely off-topic, the rules used to build the current beta variants aren't. Even if we don't know much about them. It's those rules who define the relative costs of each weapon, against which we'll judge their relative utility and effectiveness. And in turn, the relative utility and effectiveness of all variants, canonical or not.
You ask what makes a good mech in MWLL. I'd say the single biggest factor is simply ease of use, both in manoeuvrability and accuracy. But I feel like this whole thread asks if a good mech in CBT should also be a good mech in MWLL. That's a bit trickier.
If the LBX10 is buffed to improve the Thor Prime, so will be the Beatstick. How can we improve primes without improving boats?
In CBT the LBX10 has the advantage of longer range over LBX20. I never played CBT except for a few MegaMek skirmishes against AI so I don't know if it's worth it, but in MWLL it certainly isn't for me. Most ballistic weapons are not easy to use at long range, and the range gap is usually easily and quickly closed. For 2 mere tons, the increased damage is too valuable.
If ammo loaded into weapons weighted something, we'd have to choose between a LBX10 with 2 reloads and a LBX20 with none. Then I'd have to think about it. But that's not a suggestion I'm making here, because it would ruin many variants, and only promote
more laser boating.
As for the boat tax: it could work, but it's probably far too complicated with an enormous number of coefficients to balance and maintain. And it would require me to buy a new mouse.
For instance, the Thanatos Prime has 10 HS, the CBT has 6 DHS. It is not really possible to build the Thanatos prime as it is in MWLL. But let us look at it from a different perspective; 10 HS do not deal with as much heat as 6 DHS, which are four tons less. So what if we had 5 DHS instead?
I'm glad you asked that question! Because the answer will be very easy.

5 DHS is what the Thanatos already has in 0.4.x. At least that's how it appears in the XML (
<Elem idRef="idHeatTracking" name="hasDoubleHeatsinks" value="1"/>). So its 5 HS were turned into DHS, and there's no other change since 0.3.2 (aside from a generic change in armour distribution). The tooltips lie again?
Now why some primes got an upgrade and some didn't? XL engines for everyone seem to be a bigger factor than DHS, especially now that they're available to some IS chassis. And the fact that engines can only hold 10 single HS also artificially degrades many Clan Primes' performance. But it would be pretty hard to balance a fusion engine with 10 embedded HS against a XL fusion and 10 DHS. A Thanatos Prime with a regular fusion engine and single heat sinks would need to be 35t overweight to reach the same performance. (But there's just enough crits available to do that

)
And I still don't know why I hit "Reply" sometimes, because it takes me hours to post each time -_-