I agree, and in my mind, many of them did indeed exist. I could easily see the Triumph as an attempt to take the Federation-class Dreadnought and downsize it in size, costs, and materials, for instance (albeit a failed attempt).
Yeah, everybody at Oakland Shipyards, where it was designed, also think it was "just plain ugly." (Excerpt quoted from the Oakland Yards tech manual
It wasn't just the fact that it was "just plain ugly", mind you! That wouldn't have mattered if the Triumph had been able to outmatch other ships of her size (namely the Constitution class), but in addition to still lacking agility, even though the third nacelle added power to the weapons, but as the other starship classes were upgraded, there was less and less of a difference in weapons power, and the Constitution class was better rounded overall.
In the end "it just wasn't worth building any more examples of the Triumph class", and "the much later Ascension class, herself a sub-class of the Belknap-class Strike Cruiser, was more heavily armed and agile than the Triumph class could ever hope to be" (I believe these quotes comes from the Triumph's Starfleet Museum Exhibit).
And yet, somehow, the idea of mating both hulls directly would become more and more successful much later on, which was good for the Sovereign class. In many ways, the Intimidator class could be considered what the Triumph class was supposed to be.