It is the same speed as the 2017 12” MacBook
I didn't realize until you mentioned it, but I looked it up and it seems you're right.
https://www.macworld.com/article/3318566/macbook-air-2018-review.html
The Intel i5-8210Y CPU of the new Macbook Air is basically a slightly improved version of the Intel m3-7Y32 CPU of the 12" Macbook - only about 10% faster. Which is interesting because the Intel i7-7Y75 of the 12" Macbook was about 10% faster than the M3.
The Macworld article suggest to look at the new Macbook Air as basically a second-gen retina Macbook. Which is fine, but too bad it looses a lot of the neat engineering. No more latticed batteries, no more fanless design. Oh well...