FAE is the most busted of busted, 4x so on artillery cannons as it massively increases the damage and radius for almost no cost. The base LTAC is already more efficient then a clan LPL versus most mechs, and infinitely more efficient versus multiple infantry. Ive used FAE artillery when I was allowed, and it was reviled and rightfully so. FAE bombs are even more disgusting, a FAE bomber is the boogeyman used to scare children from wanting to join the house military by worried parents. A line of infantry die, 5+ hexes wide 20 hexes long if you get average scatters. If fires are turned on, good luck tracking that! I got over my FAE phase pretty quick Daryk as you can tell haha.
We play 6-10k normally. Most events have numerous comp rules, one of the more popular is 'only things found in the BMM'. BMM + elementals from BTCC (before rec guide nonsense) or BMM + vehicles, infantry, battlearmor.
One of the common 'cheese' limits is on hard to hit things, like jump 7+, and on TAG artillery. Many events allow zero TMM ignoring attacks like bombs, artillery, airburst mortars, and put a limit on how many pulse lasers you can bring. This is because the organizers want to see small fast things not instantly crippled by pulse/AOE, to encourage diversity instead of maximum armor or woods jumping.
The point of banning certain things is because in any meta, accuracy (and conversely defense) on the 2d6 curve always wins. The Blackhawk/Nova S, with its heat neutral 6 medium pulse lasers, the rifleman IIC with its 4 large pulse lasers, The goshawk 2 with the 7 jump and 20+ pulse damage, the Uziel with 8 jump and 24 pulse damage. These things were too prevalent. As I understand, even in alphastrike they started banning artillery as the arrow demolisher was just too effective on the table ignoring TMM and disapearing anything with 4 health, or 2 things with 2 health, each turn. By banning certian things, or reducing them to 1 in a list, you force people to have to take other stuff.
Elemental IIIs are pretty dang good, so it makes sense to put some kind of a cap on how much hard to kill stuff like that you can bring. Usually its 1 or 2 units max, and from what I heard when the cap was 3, the winning list was 3 units of stealth elemental IIIs. No one brought the obscure counters, and people shy away from artillery, so the stealth BA had a field day holding objectives at range. There wasnt enough turns or real life time to kill them, and they hit back pretty good to boot, while being really cheap. I doubt if the elemental III had less then 10 armor, the person playing them would have taken them over normal elementals.