Both correct?

[Shinya Maki]

Hello, everyone.

Are both #1 and “#2 correct for the blank below?
1. have been
2. were

Armed conflicts in the 21st century are less deadly than they ( ) at any time in the past 55 years, according to a three-year survey on warfare and violence.

Best regards,
Shinya Maki

[IkimashoZ]

Although technically only number 1 is correct, I think you will hear a lot of native speakers or even writers substitute number 2.