What a load of baloney. Didn't you read the other posts? They were found with the DSS that certainly predate the NT authorship.
Try the same argument against the alternative version. There is NO manuscript evidence for the Hebrew version within about 750 years of the Septuagint. Does that mean it didn't exist?
The "Spetuagint didn't even exist in Jesus' time" is a "novel" argument. What version do you think the NT authors quoted? It sure doesn't match up with the Hebrew version.