In general I think many will make the same choice as you. But sometimes the results are difficult for us to predict. Like the Napoli vs Fiorentina match, I think this is quite difficult to predict. Even though many people will favor Napoli, I think a draw could also happen. Because this week, Fiorentina will host the match.
Napoli and Fiorentina are different in their player quality as well as their experience recent years in competitions for top positions in Serie A. Napoli are more experienced than Fiorentina and in player quality, they are better than this opponent too. In this match between them, directly face with each other, I see Napoli will have better opportunity to win it, and they will collect three more points from a tough opponent, to race with Atalanta and Inter Milan for Scudetto.
The Fiorentina vs Napoli match may indeed be quite difficult to predict. Fiorentina who will play at home may also get a chance to rise after the last 3 matches did not get good results. Fiorentina can give their best in the match. They can beat Roma with a good score, if they do not play better then there is a possibility that the result could be the same as when facing Udinese. Napoli is also currently pursuing the top position
Napoli are in a Scudetto race with Atalanta and Inter Milan but if they're not careful, a position in top four can be lost to other teams. With a half of season left, with many matches, big changes can happen and it's too early to appoint a position in top four to Napoli. They have to fight in every match to get a high position in Serie A, in top four first, and if possible race for Scudetto.
And for the AS Roma vs Lazio match, I think the same as you, namely that Lazio will really be the favorite in this match because the difference in the level of consistency between these two teams is clearly visible and yes, Lazio is better this season. So I also think Lazio will succeed in winning this match.
With rising form of Roma recent matches with Claudio Ranieri, this Rome derby becomes more exciting. Roma are too far from top 6 and top 4 of Serie A, and they will need many good matches, to move closer to these high positions, so this derby is important for them, more than an usual derby. Any bad match and result from now, will contribute to a more likely bad ending for Roma in this season.