Wow dude, you are being unnecessarily argumentative...nobody's said that its ALWAYS a bad idea. I even said, if your DM bans PrCs or multiclassing, its a decent way to go. If you are PrCing heavily, you lose a lot more than you gain though. As I said, in a typical Sorcadin build (Pal2/Sorc4/Spellsword1/AbjChamp5/SacEx8), you only have 4 levels of Sorc. The difference between the d8 and the d4, on average, gives you 2 HP per level, for 4 levels, resulting in 8 extra HP. Thats not even one hit's difference at level 3-4. Considering most of your HP comes from Con and temp HP like False Life or Minor Shapeshift or a well timed Vampiric Touch from your spellstoring weapon. Also, you gain a total of 1 more BAB. Converted to Power Attack, thats ~2 extra damage per hit, with slightly earlier access to your next iterative.
Contrast with what you lose. You lose 9 spells known. 9!!!!!! Considering you only get 3 total known for the higher levels, that knocks you down to 2 each. That really hurts. That might be the difference between knowing the Heart of X line (which give you full fortification and a bunch of other benefits) and not. Negating one crit due to fortification pays off those 8 HP really quick. I mean, the whole point of playing a gish is to have spells, and using those spells to augement your combat abilities. This is intentionally disarming yourself for negligable benefits.
And if you do get stuck in a dead magic field, the difference between 14 AC and 18 AC (Mith Chain Shirt vs Mith Fullplate) is negligable. Anything with a +16 AB or higher is still gonna hit you most of the time. Not to mention that you've spent an extra ~9000g (equal to +2 Con, +2 Cha, and +1 Resistance items together) and a WHOLE FEAT for that extra +4 AC. Thats a pretty bad trade for the 99% of the time you WON'T be in a dead magic area. If your DM makes you adventure in a dead magic area all the time, you might want to reconsider playing a gish.
Nobody's saying that Battle Sorc is always a bad option, but in most cases, especially where you'll be PrCing out, it is a bad choice that lowers your options, versatility, and daily staying power. It has its place, but in a Sorcadin build is not one of them, and a Sorcadin build is what I was recommending.