Yeah, I honestly didn't know that setting the frequency to what the RAM is being sold as is overclocking.
Basically its the same as 2133mhz RAM but the manufacturer tells you its good enough to overclock?
No, 2133MHz is the DDR4 standard. That's the baseline that RAM will default to until it has been clocked differently in the BIOS or through RAM tweaking software.
Indeed, just because RAM is sold at 3600MHz doesn't mean it will run at that frequency on all setups, but the manufacturer quotes a specification they guarantee it can hit on certain setups. This is why it's helpful to look at the QVL list for your motherboard after you've decided which CPU/MoBo combo to get before ordering the RAM. Here is the QVL for your motherboard and CPU:
https://www.msi.com/Motherboard/support/MPG-X570-GAMING-PLUS#support-mem-19
The QVL is a guarantee from MSI that with your CPU that RAM will run at that speed. It's more painstaking, but you look for kits of the right size you're after (ex. 16GB or 32GB) at the speed you desire, then you can copy the model number into PC Part Picker search bar to determine the current best price.
Nevertheless, many sticks will run at their rated speed, or even higher. This is why b-die RAM is so costly. Those kits are known to run at fantastic overclocks on just about anything. Ultimately, they aren't the best value respective to their cost.
Your sticks RAM code are F4-3600C16D-32GTZNC. They don't show up on that QVL list, specifically, but you can see that every F4-3600C16D kit from G. Skill is rated to run at the promised 3600MHz. So it's weird those wouldn't automatically overclock via XMP, but at the end of the day, if you manually calibrated it to get you there, well, you got there.