BIAS selection too stonk.
The frustration with RNGesus is not understanding what kind of odds you are taking and the risk associated with it.
If you roll a coin flip situation and you lose and get mad at RNG, then you should had not taken that 50/50 if that decision makes you lose the game.
The whole game is about taking good decisions and mitigating RNG. If you are playing teamgames, subconsciously, you are putting part of your decision making in someone else making your decisions less impactful. For most, this is a stress reliever or removes an anxiety component of been the only one to be blamed by a loss.
Same with been frustrated with RNG. It's easier to blame RNG rather than one self.
<warning: I got carried away a bit>
This is how you play CoH. The whole game is about mitigation of risk and emphasising flaws/strengths rather than flat countering. Which is why I can play this game non-stop all year round rather than -say- starcraft or C&C, it's always down to chance, My friend lost a Sherman the other day to a stuG after the sherman and his AT gun firing HVAP bounced 5 times in a row. RNG is the best terrible thing about CoH but it's like a drug to me.
Sometimes you get plain unlucky, but the only time this should be a problem is when you only stood to gain from the result, i.e.- bouncing the final shot on a retreating panther. If you get unlucky and lose a unit, you didn't analyse the risk vs reward correctly or didn't have enough info in the first place to make the correct call so you didn't get unlucky, you got what you deserved. (Excluding plane crashes, this needs to be removed in the next game).
Going through @Rosbone's post, nothing personal, he's right, this is everyone's experience at some point and we're all guilty of all of it: I write this for all the usual suspects that REE in game and then stalk the forums for confirmation tbh.
If an enemy mortar is hitting you with laser-guided-nazi-uber-shellen, especially if he doesn't have line of sight, you're unit is probably stood in a place that people predictably stand in. Mortars are inherently extremely random, however if you're not hitting him through FOW and he is hitting you, perhaps he is in-fact spotting you and you just don't know. It's worth noting that mortars cannot one shot infantry models apart from with a direct hit, so if he wipes multiple models, you should probably have healed up, or retreated earlier.
If your artillery isn't hitting anything, they're probably moving away as soon as the first shot hits. Therfore you should be firing artillery at places where you KNOW they will be, fire at retreat points after they retreat or engineers that are repairing a tank and always pair artillery with frequent recon or scouting. Otherwise, true, you will never hit anything. For their artillery hitting you, remove their recon, build AA and move units constantly, sure you may still get hit but again, it's minimising risk. Failing that, doctrine choice. ML-20s and LefHs are extremely easy to counter, stuka dive bomb/IL2 bombs/air supremacy, time on target or railway/240mm immediately kill them, use them as soon as you hear the first shell fire and chances are they won't bother building another because they know what will happen to it.
As for your grenades doing nothing. One grenade is useless imo, even panzergrenadier and other heavy nades. 1 grenade will do nothing because the enemy will/should see it and move, 2 grenades, one where he is and one where he'll probably be and you'll probably get him every time. Twice the price but 9/10 times you throw one grenade, the enemy will dodge it. As for their grenades, why are you letting yourself get hit by them in the first place? simple. Unless they throw 2...
AT guns and TDs bouncing the first shot? hold fire and wait for them to come closer or get closer yourself, the more range you give them the less likely you are to pen, obvious I know, but you shouldn't really expect to pen a comet at max range with a PaK. Failing that use more mines/snares and it doesn't matter if your first 3 shots bounce, they're probably dead anyway. As for your tanks, always assume the enemy will pen, rely on health, not armour. If you rely on your health you can only be pleasantly surprised, if you rely on your armour, you will only be disappointed. Know what your tanks can take and play them as if every shot will pen and you'll never lose a tank to RNG.
If your infantry is being wiped by anything other than a direct hit from the first artillery
or tank shot, you didn't retreat early enough or you didn't heal up before engaging. There is no other side to this, simple as. If they're being wiped on retreat from max health, are you being flanked? In High level play the ONLY time a squad should really be wiped is if your enemy outplays you and flanks your retreat path.
Elite infantry not wiping a support team, either it was crewed with shock troops, in which case, yeh that'll happen, or you didn't flank it as well as you thought. *shrug* use more elite inf or just whack the weapon with artillery. Use smoke to approach and then they cant shoot but you can nade etc.
Infantry wandering about after orders, Attack-move is your friend, you should be using A-move more than attack, you shouldn't really be clicking on units most of the time anyway, I understand sometimes you need to focus fire a setting-up MG from time to time though. It's all due to dodgy LoS blockers so make sure you have clear line of sight before issuing direct attack orders.
Last one, no idea, not really experienced that. Packet loss maybe?
If a person makes a poor play, either the unit will be wiped in which case they deserved it, or they get lucky and the unit escapes miraculously. In my opinion, RNG is actually your friend. In any other RTS that AT gun would pen you every time and that mortar would hit you every time. So the only RNG in my eyes is when it doesn't.
Without trying to sound like a pretentious arse: There is no bad luck in CoH, only bad play.