Soldered RAM isn't meaningfully more reliable.

No — not in any way that matters to you. The theory is correct: fewer physical connection points means less chance of a loose contact, dust, or corrosion issue. But in practice, RAM module failures are extremely rare on both sides. The difference in failure rate is smaller than most people think, and certainly not something you’ll ever notice.

The real problem with soldered RAM is that you can’t replace it when it does fail, or when you want to upgrade. A bad stick of soldered RAM means a new motherboard — or a new laptop. Meanwhile, replaceable RAM can be swapped in five minutes for less than $50. Soldered RAM trades a theoretical reliability gain for actual repairability loss.

I would take replaceable RAM every time. The “more reliable” argument is mostly marketing to justify non-upgradeable designs. If a manufacturer uses quality components, either approach will last the life of the machine.

Don’t let the reliability myth talk you into a disposable laptop.