Datto ditched Authy a few years back due to security issues by the way, I don't know if that was ever resolved... so beware.
That's because hypothetically a criminal could call your phone carrier and trick them into mailing them a SIM card, which would allow them access to your phone number. They could then use your phone number to get into your Authy account. The problem with these hypothetical scenarios is they're so unlikely that they're not even a concern. First off, the criminal would have to know that you use Authy, know your phone number, and know what carrier you use. Second, they would have to know what accounts you have on which websites and what passwords you use, so they'd have to break into your password manager too. In addition, Authy encrypts your 2FA accounts with a password, so even if a criminal did get into your Authy account, they would need that master password in order to do anything.
Unless you're a high profile individual that has a lot of money, no one is going to target you specifically. They're going to target people with the weakest security. 2FA with Authy is still more secure than SMS, but even SMS is pretty secure. The chances of being able to charm the Verizon rep into mailing a SIM card to a different address on the account is not very likely. If they had your SSN and other info needed to impersonate you to the Verizon rep, you've got much bigger problems than a criminal accessing your Facebook account. Basically, in order for these criminals to be able to get past your SMS 2FA, they would already have stolen your identity. Why bother getting into your existing account when they can open a fraudulent CC under your name instead?
Any type of 2FA makes an account 100x more secure, as the criminals need to basically steal your whole identity in order to get past it. Authy adds another layer of complexity since the 2FA codes are encrypted with a master password, so just getting access to your phone number isn't enough to get into your Authy account. And even if they did get access to your Authy account, they would need your passwords too, which should be stored in a password manager.
In other words, most of these hypothetical security issues aren't really a concern. So long as there are people out there with weaker security, they'll be targeted before you are. Authy is going to be less secure from now on not because the technology has changed, but because the base level of security is changing, making Authy a more tempting target.