I honestly dont think leifang is just about defense in doa5, sure they did buff her defense tools like her hold but she can also win without to rely only her throws and hold. she is safe, she had good mix-up of her
string combo,guard break and sit-down stun moves and all she can be very effective as an offensive as well.
and about the throw and counter BT thingy, is pheonix said dat every move dat put in BT have a purpose but im just point out dat not all of them gurantee anything. like ayane and kokoro throws only give them frame advantage to start start their pressure.
I agree that she her offense is solid, but I wouldn't have used those examples.
Lei is faaaar from safe. The only guard breaks she has are her 6H+K and the last hit of 4PPP, which are both really easy to see coming. (O I forgot about 1P+K, but you'll rarely be having this blocked, I'll touch on that more in a sec)
Her sit-down stuns are pretty bad too. Like you said, not only is 3P4P hard to follow up, but its also very easy to counter because its 2 slow mid punches. Same with her 2P+K. Its slow as hell.
So if you want to praise her offense, I would first start with her amazing crushes. 1P, 3P+K, 2H+K, are all great. And then you have the aforementioned 1P+K. You dont want to be using it when the opponent is doing nothing. You use after you've done something unsafe or if they're being overly aggressive. Lei's animation during 1P+K will either make them whiff or go right under whatever they tried to do.
Then you have her decent launchers, and the easy, high damaging juggles she gets after them.
And if you want to talk guaranteed damage, forgot her sit-down stuns and look at 64P. I cant praise this move enough.
So yea, Lei is definitely hold/throw oriented, but she can easily hold her own without them. I would say her biggest weakness is spacing outside of mid-range. Other than that, she can hurt you in a bunch of different ways.