He just may not know... AMD exactly hasn't been on the map and if he isn't familiar with PCs then it is understandable. The i5 has been the go to for a very long time. So maybe be a bit more delicate. That being said though, I do agree with your overall point. i5s are silly now. Ryzen has completely eliminated every Intel part essentially except the 7700K and Pentiums.
We really need to know how much you're willing to spend. That will dictate what parts to choose. Since you don't need a GPU or PSU (assuming that it is of high enough wattage and good quality) that gives us some room. It would also be helpful to know what you plan to use your PC for. Is this build gaming strictly, all around use, editing/rendering, ect? Do you plan to overclock or want to? That is important.
Barring that I can't be very specific.
Right now I would suggest you grab the following
CPU: Ryzen 5 1600X.
That is AMD's latest 6 core 12 thread CPU with a base clock of 3.6Ghz and a turbo of up to 4.1. It will be very good for gaming and especially multitasking.
If you are willing to OC then get the 1600. It is the same just lower clocks and cheaper. Can easily be OCed to the same level however if you wish not to mess with that grab the 1600X. This will likely require a new CPU cooler and a better mobo.
Motherboard: Lots of choices here.
On the higher end one could go with an Asus Prime X370-A, an AsRock Gaming K4 or a Gigabyte Gaming K5. Or on the Ultra high end an Asus Crosshair VI Hero or the AsRock Taichi or X370 Pro. These are all X370 chipset boards. More PCIE, generally better built, more features more expensive.
Also look at B350 boards. Less expansion and options and a bit lower quality but they can still OC and are cheaper.
The Asus Prime B350, Asrock Fatality B350 and Gigabyte Gaming 3 are good options.
I really can't pick one specifically without budget in mind.
RAM: Really any RAM should do but you should get as high a speed as you can. A 2X8 kit of 3000 or 3200 Mhz RAM would be a good option. Ryzen reallllllly likes fast RAM. Again others can help here as they know which RAM is generally best for the platform but we need to know your budget of course.
Other than that you're also gonna wanna grab an SSD if you don't have one. A Samsung 850, a Crucial BX200 or something similar is a good option there.
You also probably don't need a new case but if you really want one the NZXT S340, Corsair 200R or one of Fractal's many offerings are good choices.