That seems a trifle harsh on GBM...
Well, that reminds me that McClellan wasn't the only shit general on the Union side.
That seems a trifle harsh on GBM... to whatever level he organzied and then commanded the Army of the Potomac, he gets (at least) credit for Antietam, which considering who was leading the ANV, seems like a reasonably noteworthy accomplishment.
As far as his subordinates in West Virginia, Rosecrans was certainly capable enough at the corps-level and below, and showed to be very effective at maneuver warfare during Tullahoma, at which point his troops - both straigtleg and mounted infantry - proved themselves quite capable of dealing with apparently best the rebels had in the west, and on the offensive, at such locations as Liberty Gap and Hoover's Gap.
JJ Reynolds rose from regimental commander to brigade, division, and corps command, serving effectively in combat at every level, and served as George Thomas' chief of staff; not exactly a slouch, either.
Kelly had a mixed record as a general officer in various garrison and security assignments; nothing spectacular, but ended up as a bvt. major general;
Morris did well with a brigade in West Virginia in 1861 and actually declined a MG's commission in the USVs, returning to the railroad industry as an executive in 1862;
Hill did okay with his brigade in West Virginia, but left the service afterwards, akin to Morris;
Cox served as a brigade and district commander effectively enough, and also ended up a MG in the USVs;
Benham had a poor record as an infantry brigade commander, but excelled as a combat engineer, and led the AotP's engineer brigade from 1863 to the end of the war, also getting a MG bvt.
Milroy had a mixed record as a brigade commander, and his division was smashed by Ewelll's corps at Winchester in '63;
Schenck wasn't much of a field commander, but was WIA in '62 and served on rear area duties for the rest of the war;
Lander died of illness in '62 after a record in '61 that wasn't especially bad or good;
Shields also wasn't much of a field commander.
So of the 11 men named, two were solid combat commanders at the corps level; one was a solid brigade commander and was offered significant promotions, but declined; another was excellent in his chosen combat arm, but not as an infantry commander; one died, one was WIA, and of the other five, two seem capable enough, based on their records. Three seem marginal.
Doesn't seem like a particularly poor cross-section; not every officer is going to command an army in the field, after all.
Best,