Compressive strength of base insulation two opinions

Hello. Unfortunately, we have a damp spot on an exterior wall and need to excavate and insulate there. We now have two offers, A wants Styrodur boards with a compressive strength of 300 kPa. B says 150 kPa is completely sufficient. Which one is correct?

For insulation in the ground up to 3m depth, both are permissible.
With the 150 kpa boards, it is probably not XPS, but EPS - this is also permissible, depending on the product but not with standing or accumulating groundwater. I would rather use XPS for insulation lying in the ground, as it is closed-cell and has low water absorption even in critical environments. The compressive strength (whether 150 or 300 kpa, both are sufficient) actually plays no role there, except under the slab.

Apart from that: Has it been clarified where the damp spot comes from? Water pipe in front of the wall, exterior sealing not present? Condensation on a cold surface?
If the wall is already exposed, in any case seal it again before applying the insulation.

Thank you for your detailed explanation, it helps me a lot! It is also true that one is XPS and the other is EPS. The assumption is that the moisture comes from a concrete path/staircase that was poured directly against the house. The path is now 50 years old and there is about a 3cm gap between the wall and the path. At the damp spot is the lowest point before it then goes straight again, and in that corner it is damp inside. We now want to tear down the entire staircase/path and excavate everything down to the bottom to reseal and insulate.