Any decent technician would know that surface oxidization is a huge issue in pressure contact solutions. Most metal surfaces will oxidize in contact with air which leads to loss of electrical properties. The most common solution to this is to add a very thin coat of gold to the contact point, which almost all modern products, including the Nintendo switch, use for their internal connectors. That's why the pins, ribbon cable contact points etc have a slightly yellowish tint to them.
Another detail worth considering is that connector pins and pads are designed to have a decently sized contact surface to improve conductivity.
The dat0 solder ball under the emmc is not designed to be used as a contact point and is not gold plated - it will oxidize and lose contact with the flex adapter eventually. How long it takes depends on many variables, but the point here is that it is not a permanent solution.
I was going to be rude here but I'll settle for a smiley: