If Signal is secure really depends on your threat model.

While they never classified them as data breaches, they had all the numbers in their system extracted number of times.

If someone was using a real phone number, even if Signal was secure — just knowing the number alone would give an attacker addition information. When Moxie was in charge, he repeatedly refused to allow new users to signup without phone, even though in there numerous ways this could have been done and are being done by their competition.

Lastly, all three Signal board members have held the top leadership role in past year, which is highly unusual, in fact, never heard of anything like it.