Are you judging by the fact that this is showing 450mbps as the max speed? Because I have just checked if the range has improved or not by taking a mobile to the other end of the apartment. No...

I have installed the free version. Can you please advise on how to get the analysis? I'm sorry but I am a noob to be honest

Latest firmware upgrade done. Different channels tried. Same old performance. Is there any way to test performance that will show for certain that the signal strength is not up to the level?

Yes. I don't have a device supporting 5ghz band yet.