It's called blowing your wad, Tony
Seriously though, you make a good point. Despite my feelings about The Zombies, I've barely listened to any Argent, because what I *have* heard has none of the old magic. And White shouldn't be overlooked as a songwriter either- he wrote several great songs like "You Make Me Feel Good", "Leave Me Be", "I Can't Make Up My Mind", "I Must Move", "I Love You", "Remember You", "Beechwood Park", "Changes", "This Will Be Our Year", "Don't Cry for Me", "I'll Call You Mine" and "Nothing's Changed".
So yeah, they had *two* great songwriters, which was maybe part of the reason The Beatles famously considered them the most talented of their British Invasion contemporaries and showed interest in producing them before they dissolved. And yes, the songs were also more sophisticated compositionally than what The Beatles were doing, regardless of differences in age