Things i need to know about Lightning.

The best thing about the Lightning is it's very flexible ans balanced: almost every setup has a reason to exist. Personally I like Fire Suppression + Auto Repair + Racer Chassis. I mainly play aggressively hit & run ans it's effective.

I also had this feeling. That's why I love the synergy with Fire Suppression.

HEAT is still unable to OHK indirectly. HEAT splash is only 750 within 1m, meaning that you need a direct hit to OHK. So if you need to directly hit them anyway, why not just take AP which also gives you a bonus against enemy vehicles?

HE still can only OHK within 1m of the target. 1m is not very much distance. It's less than the OHK range of a frag grenade. Half the OHK range of a Proximity Mine.

Sure HEAT and HE might be good against weakened infantry or infantry under fire from multiple sources, but against that "peek out from behind a rock for a second" type of infantry you're better off with AP. It's almost always direct hits with those targets because they're fighting from a ridgeline or something with nothing behind them. Against all other infantry it's up to you to pick whether you want to engage them, but peeking infantry are typically the ones shooting back at you.

nanite repair, emergency fire extinguisher, rival

thats all you need.

Don't get racer, never get it.
Anything else is really up to you, but how well this beast can survive with all this auto repair means you don't need to get out to expose yourself to enemies unless its really an emergency to repair your tank.

Also use the default viper cannon, its good all around when dealing with infantry and tanks, I used to go AP only but then as I realized I couldn't deal with infantry and then HEAT just felt too weak against both tanks and infantry, I realized that the viper is simply just good at what it is. Reducing its reload time also makes a huge impact on how much damage you pump out on enemies.

They ADD splash damage to your kill, THAT's the point. That you're damaging their allies around them. Also that you can damage infantry that try to hide around rocks, corners, etc.

Back when (not very long ago) AP had the highest velocity and HE shot like spitwads, yeah, AP was best when direct hits were all you aimed for anyways (nobody relies on 1m splash for kills... you aimd for the body not the feet) but now that you can pick off peaking infantry just as easily with the other canons as AP now, if you mainly expect to only fight infantry, with maybe the odd vehicle that you'll group up on with friendlies, then it's a worthy trade to be able to kill the peaker AND injur his buddies crouched behind the hill NOT peeking.

Vanguard needs 4 shots from the front of a Lightning to kill it with 3,5 to 4 seconds reload, TTK is 14 to 16 seconds
Lightning needs 4 shots from the behind of a Vanguard, 6 if it uses his shield with 2,7 to 3 second reload. TTK is 16,2 to 18 seconds. 1/2 AP Vanguard wins, although he's got 0,2 seconds to react to the Lightning if the Lightning has max reload and the Vanguard AP is uncerted, but both certed it goes up to 2 seconds. If he manages to turn and get even 1 shot in the side he's already won it fair and square even in the worst case scenario.

Prowler needs 6 shots from the front and has a reload speed of 2 to 2,5 seconds or a TTK of 12 to 15 seconds.
Lightning needs 4 shots from behind the Prowler or a TTK of 10,8 to 12 seconds. If the Prowler is Anchored you are completely toast, if the Prowler uses his high agility to tank a side-shot instead of a rear one he wins, if you get even the slightest bit of extra damage he wins...

Magrider will instantly turn around and has a similar DPS to the Vanguard, but now you lose your rear-attack advantage and are dead again.

So yeah, the Lightning is at a disadvantage against any MBT, and if they even have a Basilisk gunner or any other AV capable top-gun for that matter you'll lose any close combat scenario even when you attack from the back.