He is not useless overall as CSA is hard pressed to have enough ** generals in the West to form enough supporting defensive lines (strategic rating 4 is so much better than 3 also). And defensively he is not worse than Bragg and Hardee when they got promoted (isn't it sad for CSA?).
On offense though - if you have to take it - both Bragg and Hardee got stat 3 if I recall correctly - you should use them (and even avoid using Polk in support if he is more senior corps commander and there is no army commander nearby - as he will take overall command).
Regarding those 2 particular battles:
1st one:
1. You've got good numbers, and even more artillery. But the majority of your artillery was horse, 6 and 12 pounders - all quite bad at assault.
2. That coffee mill gun could cause huge havoc also - but this could be seen from battle logs only.
3. Forest terrain severely restricted your ability to use superior numbers due to frontage limitations. While Grant's superb stats allowed him to deploy the majority of is forces at once (see wiki
http://www.ageod.net/aacwwiki/Frontage for additional details).
4. You got unlucky (your luck roll was lower than your opponent's).
2nd one:
Almost the same as above:
1. More, but inferior arty;
2. Assaulting in wood terrain against opponent with very good defensive stats;
3. You got unlucky again :/;
4. Possibly assault at all costs setting versus defend at all costs resulting in lots of destroyed elements.
It could not be seen from screenshots, but possibly some adjacent US corps could have participated in the battle via MTSG (sometimes it is not reflected in battle screen, but could be seen from their diminished power ratings after the battle).