I think it absolutely should last you. The S9+ is about as future-proof as you can get, with one exception: software updates. They come late, and they certainly don't last as long as the Pixels do, which gets something like 2 years of major software updates, and three years of monthly security patches.
Unlocked Samsung devices and some of the carrier ones (namely T-mobile) have a steady monthly update of security patches, but not as often or as early in the month as Pixels get them. And for major software updates, they come months later, and you will get one, but maybe not two major updates. (Is the S7 models getting Android O?)
If that all sounds okay with you, the S9+ should last. It's pretty future-proof in nearly every other category.