Signal is a centralized, US-based service which requires your phone number (thus your real identity, IE name and address), has social networking graphs of everyone you talk to, and must forward that information to the US government when asked, as well as (by law) not tell you that they've been asked to do so. During the Obama era, 60 NSLs were issued for this private information every single day.
People overlook its privacy concerns for the same reason they do with apple: it has a shiny interface and is easy to use, and makes people very attached to it. Behind all that, is a surveillance network that its creators have explicitly said they do not want it to be able to run in a decentralized, private manner.
It has a long history of privacy offenses below (such as refusing to publish its server's source code for years, its reliance on other US tech services (amazon, google), US-government funding, and a US-defense-tank friendly administration) which get ignored or shouted down by many of those above. See the article below.
Pretty much any alternative is better, as long as its not hosted in a five-eyes country, and especially if it doesn't require phone numbers or real identities like signal does.
I personally have been using SimpleX for friends and real life contacts, and Matrix for larger more anonymous group chats.