I've owned both the 12" MacBook 2017 and the 13" MacBook Air 2019. In ordinary daily use of mundane applications, the performance is about the same if you are not multitasking.
When you start multitasking doing multimedia work (image editing, video, audio), the shortcomings of the fanless MacBook become very apparent as everything starts to get sluggish.
This is even more starkly obvious when you encode video on the 12" MacBook 2017 as all of the CPU cycles go to this task.
On the 13" MacBook Air 2019, video encoding and decoding (both H.264 and H.265/HEVC) are handled in hardware by the T2 Security Chip instead of the CPU. Since this system has a fan, it will turbo boost and run at a higher frequency at the expense of a noisy fan. You can still do other stuff pretty well while the system is encoding video.
None of this shows up in the typically quoted benchmarks. In fact, this is an excellent example of the shortcomings of benchmarking.
And the MacBook Air's keyboard blows doors on the joke of a "keyboard" [sic] that is installed on the 12" MacBook 2017.
Carrying around the 12" MacBook 2017 was lovely. Actually typing on it and trying to get some work done was not such a joy. I quickly dumped it when the 2019 Air was released.