gpu is not working correctly or dead .

So i had this thing when i bought my rayzer laptop from off market reselled by rayzer but to another contery as they said to me at the time , the preformance was not that good so i looked it up i had a heat issue at first so i went and followed every step to lower my voltage and est. to cool down the device and it was caused by the cpu after i fixed the cpu heat issue it appered that the cpu was not the only issue the gpu is working but it’s preformance just like it’s not there » i play for example cs2 on low every thing and 1080p (even tho my screen is 1440p to get like 50-60 fps) some times 65 witch is not acceptable at all right ? i updated the bios and every single thing that i can upgrade when i installed msi after burner to stress my gpu by the kombustor it gave me like 6-7 fps on 1440p so i just lossed my mind actually and lost hope in this case (like my gpu is dead but working ?) 
i can upgrade it by the invidia exp. app but the preformance is just not there u might say may be it’s bc of 
optimus i changed it by synaps app to gpu only and from the system and from the invidia control and by 
the system > display > graphics and changed leauge of legends  to high preformance the next game i played 
on 40 - 60 fps with drops reached 14 and the laptop plugged in.

mentions might help : 

1- my laptop specs 
i7 11th gen 
3070ti rtx 
16 gb ram orignally i added 8 so it’s 24 
m.2 1TB 
screen 165Hz 15.6 QHD  (1440p)

2- the only thing that i need to mention that the battry it’s not the right one i think it’s for the base modle but with the same serial No. the device don’t detect it fully just play for 2-3 min on battry before it die + with no percentage moving or anything stuck at 100%  the thing is that i + i had this problem before i changed the battry with this one bc the last one swollown bc of the heat  i replaced the battry myself cuz the laptop is already out of warrenty 
and it went greatly no issue in that even changed the thermal pased to a good one (but no to liquid metal) 
so yee i need help in this idk what is the problem i hope if u can help me . 
Thank you .