I'm still getting a feeling for CW decks, but I have some observations.
First, the Clans can put out waves after waves of Stormcrows and Timber Wolves (the optimal Clan deck is pretty much 3xSCR+TBR with some variations involving HBR and MDD). These 'Mechs are hard to take down and do a lot of damage before they go down, even in inexperienced hands. With this deck, the Clans teams keep a constant firepower and tank on the field as the battle progresses, while the IS players are forced to bring 'Mechs like lights or silly mediums/heavies at least once to face these, potentially tipping the power scale in Clans' favor. We need IS decks with such firepower that these SCR/TBR blobs can be dealt with some efficiency.
Also, the current maps with their wide open areas favor ranged weaponry more than brawling, so the advantage goes to the Clans again.
When it comes to 'Mechs, in my opinion, the IS heavies are just not up to snuff with their Clan counterparts. None of them are particularly tanky, most of them can't boat energy, and the ones which can have huge flaws in their design. Some of them can be glass cannons (Dual Gauss Jager/CTF, ridiculously quirked Dragons), but they lack the tank to outlive their Clan counterparts. Some of them can outbrawl the Clans, but brawls rarely occur. On the other hand, the IS side has awesome lights/mediums and assaults. I think an optimal deck should focus on these classes.
We also need to consider which weapons of the IS are very effective. Since the CW maps involve mostly medium to long range combat at the moment, we need to look at weapons packing punch at range. In the laser department, IS LL and ML just lack the range and punch to be effective in these maps. IS LPL is on the other hand, is one of the best lasers in this game when it comes to punch, but lacks the range.
The best the IS has to over the Clans are ballistics and LRM's. Especially IS AC5/UAC5 are arguably one of the best weapons in this game. Excellent speed, damage and fire rate. AC20 also falls into the LPL category, packs a punch but lacks the range. IS LRM boats also beat Clan LRM boats not in firepower, but in damage application. Clan 'Mechs usually have more surface area than IS 'Mechs, so they're more susceptible to the huge burst damage of IS LRM's.
With those settled, an optimal IS deck should involve these 'Mechs and weapons:
- 'Mechs: A/A/M/L, A/M/M/L, A/H/M/L. As many capable assaults on the field as possible. Mostly snipers/LRM with a few SRM "shock troops" in reserve for objective combat.
Also the 'Mechs should be chosen for those with as many high mounted hardpoints as possible to utilize cover efficiently. Considering "good" 'Mechs, this leaves following mechs in each category.
- Weapons: ERLL, LPL for trading with laser vomits. AC/UAC5 and AC20. Dedicated ALRM boats.
- Assaults: Stalker (LRM/Laser), Battlemaster (LRM/Laser), Banshee (Laser/Ballistic), King Crab (Energy/Ballistic/Missile — general purpose annihilator).
- Heavies: CTF-3D (Dual Gauss/Poptart). CPLT-K2 (PPC/Ballistic sniping). No glass cannons like JM/DRG/QKD/CTF or brawlers like the Orion.
- Mediums: Shadowhawk (Ballistic), Griffin (Shock troops/SRM brawlers for the last objective), Cicada-3M (Laser/PPC), Hunchback-GI/4G (Gauss/AC20), Kintaro-18/Golden Boy (LRM)
- Lights: Raven-3L (2xERLL), Spider-5D (ERLL, scouting, ECM coverage), Firestarter-A/H (Laser, close-mid range backstabbers). Other lights are last resort fillers only.
It gets easier from here, the builds are up to you, as long as you adhere to the 'Mechs and weapons up there. For example, an optimal deck could be:
Ballistic-heavy face melter deck:BNC-3E (3xAC5+4xML/3xAC5+2xLL), SHD (2xAC5/UAC5+2xML), GRF-3M (4xASRM4+2xML), Firestarter-H (6xML)
Laser-heavy endurance deck:STK-3F (4xERLL+23DHS), BLR-1G (4xERLL+2xLL), CDA-3M (3xERLL), SDR-5D (2xERLL)
Lurmageddon deck:Your Stalker of flavor/BLR-1S (2xLRM10+2xLRM15), 2xKTO-18 (5xLRM5), VND-1AA (ALRM20+Tag)
Annihilation deck:KGC-0000 (2xUAC5, 4xERLL), BNC-3E (same as above), LCT (whatever), COM-2D (for ECM coverage and general annoyance)
Balanced deck:BNC-3E (same as above), GRF-3M (3xASRM4+2xML), HBK-4G (AC20+2xML), CDA-3M (3xERLL)
Just some food for thought. I'll probably improve upon this as I play more and have more time to think about it.