I bought a new Xros 4 nano for 32$ at a local b+m but it seems underpowered with the .4 coil, at 30w
That's likely because pods have no buck/boost (aka step down/step up) circuitry, only buck, and because the electronics in your pod
device are likely very inefficient.
Also due to lack of boost, you'll feel the power output diminish as you deplete the battery, just like
vaping on a mech. It may even seem to be less power than a mech because with a mech you don't have the inefficiency of any electronic components to deal with (you are working straight from the power source) escpeially of all contacts are squeacky clean, and is also why your buck/boost mod seems more powerful (has more efficient electronics).
If available, you can try using a lower ohm coil and this may seem more powerful as you may never need boost, only buck. But due to highly inefficient electronics in the pod, it may still seem underpowered compared to box mods when comparing the ohms to wattage setting, but may get you closer to what you know 30W feels like on a mod.
People who have only used pods and never used buck/boost vape devices never realize the under-powered nature of their pod devices as they have nothing to compare it to.