Is less than 2 hours of battery life normal for Galaxy S2 with Screen darker than | 5 times darker than normally possible thanks to Screen Filter app,
removed more than 70 system apps (I have less than 40 now) with the rest except absolutely essential being frozen,

WiFi GPS and all the rest turned off,sound muted, CPU and GPU undervolted and underclocked,(flashed 4.4.2 ROM and Dorimanx 10.43v98.4 Kernel which noticeably boosted battery life, especially after tweaking with the settings) disabled error reporting and everything else battery using I could think of while playing any game?

I doubled the battery life thanks to all the changes I made (read above) because the battery lasted barely an hour, often less.The issue was ever since I got the phone and I thought it was caused by the Samsung bloatware and Android 2.3.4.Being very UNsatisfied with the battery I bought a new one and it doesn't help except that I have double the battery life again (4 hours max) which is still very bad for Me.

The screen gets hot but the battery is even hotter and the area around the SoC (CPU, GPU etc) gets the hottest, I believe

So is this normal? What else can I do apart from the improvements I wrote above to improve the situation?
To be honest, it sounds like a hardware fault in the phone, especially since you say it's been happening since you bought the phone. If the phone were still new, I'd say you should take it back to the shop, but by flashing a new ROM you've voided the warranty.

To answer your question: no, it's not normal for that phone. I've known a few Galaxy S2 owners, and you should get as much life out of it as any other smartphone: a couple of days between charges if you don't use it heavily.