That's may correct. What matters is single thread performance.
Take a look here: https://www.cpubenchmark.net/singleThread.html
It gives you a overview about single thread performance.
Your CPU i3-3120M has a score of 1285. Btw: Its a Sockel G2 and easy to upgrade. A 4th gen i7 QM for just 25$ would be a great performance boost.
The Xeon X5670 in my build- released in 2010 ) has a score of 1345 that's not much more than yours and APB is working perfect on it.
Link to my cheap build: https://valid.x86.fr/h9dzt3
Whatever throttles your performance. Its not the APB engine.
Maybe its your outdated windows, GPU drivers, other drivers or installed bloatware/adware. Maybe even a mix of everything, but its not the APB engine.