I guess Rupert Holmes was just a talented musician and songwriter who was trying to make it any way he could. He would have been 23 when he wrote Timothy, but he had been working in the music business for a few years before that. His talent level got him hired by some semi-important bands, and he must have been pretty good at networking. His reading of the market opportunity (as you relate it) was pretty clever, no denying it. He got a break and ran with it.
You're right. The Prisoner theme is my all-time favorite TV theme.
Holmes co-wrote and performed on a 1969 Top 40 hit called "Jennifer Tomkins" which features the lyrics below. You have to be a real old-timer to remember this one:
Jennifer Tomkins was born on a Sunday
Her daddy got drunk, and left home on a Monday
Her mama died young when Jenny was seven
And Jennifer Tomkins went to work at eleven.