Obviously a top spender will become a top competitor sooner rather than later. The question is, whether we want to have strong competitors and accept the fact that winning will be extremely difficult or be satisfied with being a big fish in a small pond.
Having strong internal competitors would benefit Juve in my opinion. Stronger league brings more spotlight and more spotlight brings more money. Juventus has top pedigree and huge fan base to take advantage of such situation.
Take a look at what Liverpool has become. They don't have the resources of City, Chelsea or United but can't be considered inferior in any competition neither to the aforementioned teams nor Bayern, Juve, Barca, PSG or Real in the Champions League.