So, you're okay with your guitar tone in isolation but not satisfied with how the full mix comes across. As others have indicated, in general the bass is what fills out the low end while the guitars give the sound its teeth. Of course, the bass drum adds to the low end punch as well, especially when carefully timed with the guitar and bass. There is definitely a synergy going on here where the whole ultimately ends up greater than the sum of the parts. It really is rather magical when happens, when everything comes together in just the right way. It's exactly why some people pay a professional recording and mixing engineer to work a little studio magic. Compression, EQ, and other post processing touches also play a role in "gluing" the mix together and helping it sound polished and professional.
From what I understand, recording great sounding heavy rhythm guitars is one of the more difficult challenges to master. It all starts with the tracking, mic placement, amp settings, etc., but by no means ends there. I'm no professional to be sure, but I have been thoroughly enjoying the journey as I continuously work on my home recordings and watch them improve little by little over time, gaining new insights along the way about the interactive nature of all the parts. It is truly a marvelous puzzle to sort out.
The same YouTube guy (SpectreSoundStudios) that made the video on the Heil PR30 has also made several other videos on recording technique such as the following video on How to Record Heavy Guitar. These videos give many useful pointers.
RT member Simon (aka, ThyFinalPain) is basically an expert at recording super heavy guitars. Everything he does sounds so thick and heavy. Here is a video from him showing the significant impact of mic placement (just one important piece of the puzzle).
Now, just thrown in bass, drums and some cookie monster vocals and you're good: