Yeah, Or he could have just been crazy like Hitler.
I don't buy that Clark wasn't the one behind his rise to power. One of the scant few times we did see him he said, "I've wanted Santiago dead for so long.....", indicating he wanted to be President (or more likely dictator) and take over Earthgov.
Nobody is saying he wasn't murderously ambitious, but nobody pulls of a coup like that without *major* support from more powerful parties. Once you cut though the propaganda and the myth-making, it's not hard to see the patterns in history when it comes to coup d'etat. When the righteous army of the people storm the palace gates to lynch the evil tyrant, it's almost always because the army *let* them and they only do that when the "evil tyrant" hasn't been looking after his Generals as well as he should.
When the upstart Prince murders his father and claims his throne, it's usually because said King displeased someone powerful within his own court, who then arranged for the King's Guard to be looking in a different direction the night Kings son pops round for a visit, blade in hand. Incidentally, the only way the crown stays on said Prince's head for long is if those self same people who helped him coincidentally get a sudden bump in their net worth.
No King, no Emperor and no President rules alone. They all need the support of powerful people who control vital resources. Money. Food. Transportation. Armies. Information. Trade. Those people need to be kept happy or the usurper will quickly find out exactly why it was to easy to knock off his predecessor in the first place.
In the case of Clark, he needed the support of people like Edgars and the other Mega-Corp CEOs, of key figured in the military and EarthGov and yes, the Shadows, though the extent of their direct involvement is never made 100% clear. Morden certainly had dealings with the faction of Psi Corps opposed to Bester's people, but whether that was direct control or merely another exchange of "favours" is not spelled out.
IIRC it's established that Morden was part of or at least working for the group behind the Syria Planum incident (also Department Sigma, EF New Technologies & IPX), so when the Shadows acquired his services, they had an instant "in" with them. Given that they were still around by the time of Crusade says to me that the Shadows never tried to take over their operation, merely helped serve each other's interests. Ever wonder how they integrated Shadow tech into the Omega prototypes so fast? Maybe "someone" lent them an owner's manual to Shadow tech.
Clark's ambitions were personal. He wanted to be in charge. He wanted power and he didn't care what it took to get it or keep it. But I don't think he had much of a long term plan beyond "stay rich and powerful until I die happy of old age". The same cannot be said for those that helped sponsor his rise. They allowed him to take power because it served their interests and their goals were clearly much more wide ranging and long term than the ambitions of a petty dictator.