You're welcome. I am all for debate on an idea and yes I am sure our games differ.
As for the CR system, I think it partly falls apart because of the premise that magical items aren't needed, but yet most games play with them. If you take out the magic items in the storm giant rock calculations, for example, the wizard's AC drops dramatically to AC 16 (mage armor, DEX +3), and AC 21 with shield... so the odds of breaking concentration rises. Also, take out feats and MCing (so no wizard's with CON saves), and now breaking concentration is much more likely!
I'll post after my group discussion later today, so you'll know what their responses are.
Cheers!