I would bet Guardiola and the City staff expected -and were prepared- for a completely different situation at the Vicarage Road Stadium...
If the people running the club (opportunists of the worst kind) sacked their manager hoping it would serve as a shock short term, well their wishes were fulfilled but at the opposite direction: Morale was unbelievably low, as you say they surrendered as soon as City scored the first goal...
Players like Doucoure and Pereyra seem shadows of themselves, you almost feel sorry for others like Mariappa, Sarr played 90' offering absolute zero, and so on, and so on. While the new guy on the bench seems totally out of his depth (by the way, our 3rd goal wouldn't probably have occurred if he hadn't moved one of his central midfielders to the right)...
It was down to the usual suspects, Dawson, Deeney, Foster etc. Again. Deeney probably faces depression, the guy has had enough of this shit, year after year...
Watford fans? You don't want to be in their position, my friend, trust me. Watford are probably the second worse team in the league, Vila being the worst (after having spent a fortune in the transfer market last summer, by the way). They've contributed absolute zero to the game this season, and they're both worse than Norwich, who paid severely for their inexperience and naivety, as far as I am concerned. Now how about looking a bit higher at the table? Sheffield Utd and Burnley have 54 points, both above Arsenal (!!!). Southampton have 49 points. I could go on but I'll stop here. That's 3 clubs already, like 15 (!) and 20 (!) points above Watford, respectively, comfortably surviving the PL this season. An outcome which has very little (or nothing, according to my humble opinion) to do with quality in terms of personnel. It's not exactly the superiority of Sean Dyche's human resources the factor justifying that 20 points gap between the two clubs, is it? The answers have to be sought elsewhere...
That's how complicated modern football can be. And that's how clueless and incompetent Watford's management is...