Unless you have coordination with the network operators on which those amplifiers are sitting, your null-routing of the amplifier in your own network isn't going to stop it from attacking other targets. If the amplifier is something like a DNS server, then your collateral damage isn't just "adjacent customers", it's potentially thousands of other users and resolvers on your own network. If those amplifiers are on a cloud service provider like AWS, you're going to potentially inflict even more pain onto your own paying customers who will no longer be able to communicate with AWS. You will essentially perform the DoS they were aiming for.
Unless you have coordination with the network operators on which those amplifiers are sitting, your null-routing of the amplifier in your own network isn't going to stop it from attacking other targets. If the amplifier is something like a DNS server, then your collateral damage isn't just "adjacent customers", it's potentially thousands of other users and resolvers on your own network. If those amplifiers are on a cloud service provider like AWS, you're going to potentially inflict even more pain onto your own paying customers who will no longer be able to communicate with AWS. You will essentially perform the DoS they were aiming for.