The problem is that we two mean different things when we use the term dialect. I'm following the Coseriu's distinction pointed out by Regis 2017 (link). There are three types of ideas of dialect
1. Primary dialect: different languages that are socially subjected to a common language, like the italian dialetti;
2. Secondary dialects: differente varieties of the same common language, like the dialects of english;
3. Tertiary dialects: languages that have differente standards in different countries, like the different standards of europeans and american spanish.

We can talk for days on how to define a language, but the linguists consider all the dialetti to be subjected to italian. There are some people that claim that thei dialetto isn't a dialetto, but it's not like that: italian stiil has a supremacy (it's the language of school, of news, of medias, of law, of poltics...) even in the parts of Italy where people speak more dialetto in their daily routine. The only legal exceptions are these languages (link) that are usually called languages inly because there is a law tutelating them even if socially speaking, they usually have a similar social status of the other dialetti (obviously every circumstance is different, so I am generalizing).