There isn't actually a 2018 model. You have a late 2017 that you bought sometime in 2018.
But that doesn't matter.
Geekbench thinks your current 2017 21" scores 3035 in multicore, while the 2019 scores 3268. Not a huge improvement (like 9%), but it's still an improvement. In single core, the new system gets 920, the 2017 gets 868 (also about 9%). So, again, not huge but still faster. The GPU will also get a small kick. The 2017 will have a faster drive due to its Fusion, but that doesn't seem to matter.
Either way, you're getting a newer system to replace an old one at no cost to you, and that is kudos to Apple. That will have an effect some time in the future when Mac OS 10.20 or something renders the 2017 obsolete but not the 2019.