If you've got enough cynicism to decide the only beneficiaries of QUIC are just "adtech companies" then I suggest saving a little of that cycnicism to put scare quotes around that word "security" in the second half of your sentence.
If you have effective security neither TLS 1.3 nor QUIC change anything in that regard. But they probably do change things for you. This means you did not have effective security.
Those making appliances or software to deliver "security" would very much like you to blame the designers of QUIC or TLS 1.3 for the fact that their products are ineffective. It is as if the Carbolic Smoke Ball Company had tried to blame doctors for diagnosing Carlill with Influenza rather than accepting that, in fact, Carbolic Smoke Balls don't work and so they owe her £100 per their advertisement.
If you have effective security neither TLS 1.3 nor QUIC change anything in that regard. But they probably do change things for you. This means you did not have effective security.
Those making appliances or software to deliver "security" would very much like you to blame the designers of QUIC or TLS 1.3 for the fact that their products are ineffective. It is as if the Carbolic Smoke Ball Company had tried to blame doctors for diagnosing Carlill with Influenza rather than accepting that, in fact, Carbolic Smoke Balls don't work and so they owe her £100 per their advertisement.