The heavy support section is one of the populated sections of the codex, with a number of good units and some not so go units. While there are some units that I think need some work to get them up to a more competitive level, there are also a couple of units that I think will see some characteristics changed due to streamlining. I'll start with these units, as they will be quick to deal with.
The two main units that I think will see some changes are the Basilisk and Manticore, and the main change will be the damage going from d3 to a flat 2 or maybe 3 damage, although 2 would be more likely. This is due to some other weapons loosing their variable damage characteristics, which is good as it gives a more accurate estimate of damage dealt. I think this is most likely with manticores as a way of reducing the effect of Full Payload manticores.
There are a few other units that need a few adjustments in my view. The Leman Russ Battle Tank, while the main tank is pretty good and not much needs changed, if anything, there are a few of the weapons options that need looking at. The Executioner plasma cannon, which follows the same profile as the standard plasma cannon with the exception of d6 shots. This means that you could end up getting just 1 shot, practicality the same as a standard plasma gun, for a weapon that is supposed to be a tank mounted plasma cannon. I think the shots need to be changed to a 2d3 or d6 with minimum number of shots, say 3. This give it the feel of a proper tank mounted gun. The other option would be to increase the strength, just 1 up, to S8 and S9, giving it that extra bit of punch and bringing it inline with the marines macro plasma incinerator. Personally I think more shots is the way to go, rather than extra strength. This would mean that the tank as a whole, with sponsons, could put out a significant amount 9f firepower. The 9ther version of the LRBT that needs looking at is the Exterminator and it's Autocannons. At present it's two barreled autocannon kicks out just 4 shots, the same as two separate Autocannons carries by guardsmen. Being vehicle mounted it should kick out more shots, in my view, double the number, although 6 would still be better. If marines can carry a 3 shot version around by hand, then a tank should be able to do at least the same, if not more. Again, I don't think that extra strength or ap is needed, just more shots, the guard is, after all, about volume.
Talking about volume, we have the Wyvern. Now, I love this weapon, it is a good weapon but as I have said before several times, it needs something more, because right now the only thing that makes it better than mortar equipped heavy weapons squads is that you can take more of them. Simply adding an extra point of strength or ap would make all the difference and make them stand out from regular mortars. I think the ap is the way to go, keeping them as S4 with re-rolls to wound. An alternative route would be extra special rules, such as re-roll number of shots or ignoring cover, even going back a few editions and being able to add one to BS if you can see the target unit (advanced vehicle mounted targeting units?) Either way, I think that it needs something extra.
Next we have to fun one, the Deathstrike missile launcher! Now, we all know that the Deathstrike is not a competitive choice, not can the tabletop model ever represent what we read in books, after all, if it did, firing one on the tabletop would wipe out the gaming hall, not just your table! The biggest issue with Deathstrike missile launchers however is the random number of shots and BS. With 3d6 shots and a 4+ BS your looking at just 5 hits. For a single shot super weapon that you can't actually fire turn 1, 5 hits is pretty rubbish. Even with the possibility of extra hits on nearby units, which is slim, as by the time.youanage to fire it most units are going to be out of range of other units, so you might get to roll 2 other dice of which one might hit and get 2 mortal wounds. Against marines, this will mean 3 and a half dead models, not a great return. I think this model needs either a big price reduction, significant damage output improvement or auto hitting shots, maybe even all three! The death strike probably shouldn't be a competitive choice but it should be a devastating one.
Next up we have what I think is the unit that needs the biggest improvement, not in terms in the units price or stat line, both of which I think are fairly balanced. The biggest issue is the restrictions in match play, know as the rule of 3. Heavy Weapons Teams are a staple of guard units, however they have been severely restricted by the rule of 3, far more so that vehicles. This is because the rule states you can only take 3 of each data sheet, and with guard vehicles this means that you can actually take 9 vehicles due to the squadron rules. Only Manticores and Deathstrikes don't have the squadron rules. This means that taking heavy weapons squads only happens if you've spare point not spent elsewhere, which is rare. I think that either heavy weapons squads need to be allowed to take more teams, at least 5, if not more, up to 9 (3 lots of 3) or we should be able to take them in "squadrons" or multiple squads in a single slot. This would mean that they would become a usable force again.
I also mention here an additional unit that I think needs adding in, the MT scions heavy weapons squad. I've mentioned scions needing heavy weapons in the troops and transports post but I think that they need a dedicated heavy weapons squad as well. I still think that these squads should have limited weapons options but I also think that they should have unique choices, such as multi-melta's and maybe even plasma cannons. The squads should follow the same rules as the standard HWS, as these could well be the only long range heavy hitting weapons and main anti-tank weapons in the army.
The last thing to mention here are the super-heavy tanks. Now, in general these are fairly balanced and don't really need adjustment. One thing they do need however is a boost to their saves, in the form of an invulnerable save. These vehicles, while tough with lots of wounds, are still fragile for their size and cost. An invulnerable save would be perfect for them. I'm not after anything crazy, just a 6++ would be perfect, just something to ensure these prized relics have a save. I'm not expecting Knights level of shielding, but just a little extra would be useful.