The Minimoog and Prophet 5 are both from the 1970s. Despite the Minimoog's status as a collector's item today, it had roughly the same retail price as the DX7 in the 1980s--around $2000 USD. The Prophet 5 was more expensive at $4000, but it was also an incredibly successful, flagship synthesizer.
Of the synthesizers listed--Prophet 5, Oberheim OB-Xa, and Minimoog, only the Minimoog was made primarily out of discrete components. The others relied heavily on integrated circuits from SSM or CEM. (Obviously they all contain discrete components--but the synth modules in a Prophet 5 or Oberheim OB-Xa are basically ICs with some support circuitry.)
Sequential went out of business after developing the Prophet VS. Although it bears the "Prophet" name, it is a digital (or hybrid) synthesizer. It uses wavetables (like the PPG), but four of them simultaneously, with a Curtis VCF. It had a novel architecture (therefore confusing), the synthesizer itself was expensive, and there were some QA issues. It used TMS DSPs plus some custom ICs designed by Sequential. Apparently, during the design of the Prophet VS, there were various problems with the ICs that were fixed with kludges--Sequential wasn't in a financial position to make revisions to the ICs.
In other words, the R&D cost for digital synths was too high.