Aside - in an older RPG history, my character was assigned to the USS Horatio for seven years, from 2356 to 2363. I started there as a junior operations officer, ultimately running the ops department before taking an extended LOA to take advanced command track courses at the Academy (with a promise from Captain Keel that once I returned I'd be in line to become his next XO). The guy who replaced me ended up being the one who brought those parasites to the ship, ultimately resulting in her destruction. Guilt trip ahoy.
Back to the idea of the Horatio as an Ambassador variant of the Probert design, I'd also say no. Perhaps at the time they had intended for her to be as such (in dialogue she was only referred to as a heavy cruiser), of coruse they had no intention to build a model for the episode we saw, so it could have really been anything. However, the infancy of the TNG-verse at the time suggests that whoever wrote Worf's dialogue could have been reading the fanon of the time and was thinking that the Horatio would be the equivalent of the Constitution Heavy Cruiser in terms of her capabilities and import for her era. When Okuda and co. retroactively made her an Ambassador class and the same class as the Enterprise-C, of course it would fit.