An adjective to describe the state of being complex yet ineffective
Since you asked for an engineering application, consider:
Over-engineered — Collins Dictionary
adj. unnecessarily complicated
"systems are unreliable, manuals are impenetrable and products are over-engineered"
Overengineering — Wikipedia
Overengineering (or over-engineering) is the designing of a product to be more robust or complicated than is necessary for its application, either (charitably) to ensure sufficient factor of safety, sufficient functionality, or because of design errors. Overengineering can be desirable when safety or performance on a particular criterion is critical, or when extremely broad functionality is required, but it is generally criticized from the point of view of value engineering as wasteful. As a design philosophy, such overcomplexity is the opposite of the less is more school of thought (and hence a violation of the KISS principle and parsimony).
Also worth reading: You aren't gonna need it.
Kludgy or Kludgey, from Collins
awkward or makeshift and poorly designed
The Free Dictionary defines the noun kludge as
A system, especially a computer system, that is constituted of poorly matched elements or of elements originally intended for other applications.
A clumsy or inelegant solution to a problem
TFD says that the origin of the word kludge is
Probably alteration of mid-20th century American military slang kluge, complex device with a simple function, perhaps of imitative origin or perhaps after the Kluge (paper feeder), a piece of printing equipment first manufactured in 1919 by Brandtjen & Kluge, Inc., and reputedly difficult to repair. (emphasis added)
Byzantine
- of or relating to Byzantium, the Byzantine Empire, or the Eastern Orthodox Church.
- (of a system or situation) excessively complicated, typically involving a great deal of administrative detail. "Byzantine insurance regulations"
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convoluted
- (especially of an argument, story, or sentence) extremely complex and difficult to follow. "its convoluted narrative encompasses all manner of digressions" synonyms: complicated, complex, involved, elaborate, serpentine, labyrinthine, tortuous, tangled, Byzantine; More
- technical intricately folded, twisted, or coiled.
Google convoluted