There are a few caveats regarding that but it is quite true that if the soldered wire bundle is not compressed enough to deform and completely fill the available clamp space, it can create a thermal cycling fatigue problem.
Soldering the wires will only make that more difficult to achieve.
And as I have said, these particular connectors are demonstrably inadequate for the currents involved with the bed heaters to begin with.
Even for smaller printers than these.
They will get hot and cause thermal expansion/contraction issues.
Back to the point though, crimp-on ferrules are the only way to go if one insists upon running 20+ amperes through the main board using these connectors.
If you look closely, all "power" connectors are rated for some number of amperes at a given temperature rise.
That is the real key to the puzzle.