QB rating isn't a "rule". It's a measuring stick to determine how effective a QB is. And it's lacking. Most people agree it's very much an imperfect tool. The question is, is there such a thing as a perfect tool? (No)
So changing it to make it better isn't "wrong". I don't even nessecarily disagree with the premise of adding in rushing stats. QBs like Drew Bledsoe who get sacked a lot are less effective then QBs like Drew Brees but the sacks don't show up in the stats. And QBs like Vick who are multi-threats in the redzone don't get their rushing TDs added either, which is unfair.
The problem is the Falcons fan who posted that didn't explain his new formula for getting those ratings. They looked awfully homeriffic and didn't make much sense.
I think the "adjustment" I did is probably the best way to include rush stats.