Actually, the 26A mods go the other direction: they sacrifice Endurance and a little bit of Power for a lot of Willpower. Due to the endurance sacrifice, they have a higher DPS-affecting stat budget than the unlettered mods.
Actually, they don't. The A variants have middling Endurance, a miniscule amount of secondary stat, and a lot of primary stat. The actual itemization budget for DPS attributes is worse than the unlettered variant and only slightly better than B variants. It's for this exact reason that pretty much everyone outright prefers the unlettered mods (some tanks like the B variants for the higher Endurance but not all; all DPS and healers should prefer unlettered mods).