Did you really think that the NT stories having OT backgrounds is evidence against them having been historical, especially when some of them (e.g., the last supper) is recorded by people like Paul who say that he is getting information from eyewitnesses of Jesus, or the crucifixion, which is recorded in extra-Biblical and independent accounts like Josephus (see my post) and Tacitus? For example, in the last supper tradition, Paul uses the word paradidōmi (see, for example, Luke 1:2; Rom 6:17; 1 Cor 11:23; 2 Thess 2:15; Jude 3) and paralambanō (Gal. 1:9; Phil. 4:9; 1 Thess. 2:13; 4:1; 2 Thess. 3:6), both technical terms for the authoritative transmission or the reception of apostolic testimony to Jesus. So Paul is claiming that the last supper teaching was the teaching of all the apostles, some of which viisited paul's own church in Corinth (cf. 1 Cor. 1:12; 3:22; 9:5). Paul says he met with Peter and James in his first visit to collect eyewitness info (see historeō in Gal. 1:18-19), and later on for different purposes (e.g., Gal. 2:6-9).