That was never an issue for Serie A teams in 80s and 90s.
Competitive league doesn't have to be throw away games in Europe.
What PL has is more expensive players that aren't necessarily better, except the ones at top 3 teams, than players in other leagues, especially considering that they bring these exact same players literally from Bundesliga,La Liga, and Ligue 1.
While Serie A was as competitive if not even fiercer at the top end of the table back in the day, the lower end of the table was less a banana skin because unless being invested privately, or some how got a golden generation from the youth system, it was difficult to break rank because media payment was poor, back then and even now. It's more difficult to get transfer through, so the investors wouldn't pick a team like City. Instead, they need to pick a team that's already have some sort of attraction/a decent base rosters.
Serie A might be attractive, but without open transfer policy, the teams at the bottom didn't have resource, and freedom to transform themselves and being a nuisance.
Serie A during 80s, 90s and early 2000s was a 16 or 18 team league. So they played less game. The 20 team league system was only reestablished from 2004. Also for the large part of Serie A super league era was under 2 point per victory system. Teams were even more pragmatic.
Basically, played fewer games in a season, less banana skins, less stamina demanding; so they didn't lose focus in Europe (also fewer games in European competitions) with adequate investment