Eddy currents are a real thing, I have seen several instances of damage by them.
The worst case was on the LV box of a 2MW transformer, four conductors per phase all neatly grouped by the phase and taken through a steel plate. The paint on the plate had burnt off around the cables and discoloured the steel. We changed the gland plate to brass to solve the problem. Interestingly at the other end the singles were again taken through steel into the switch board but there was no sign of heating, I think this was due to the singles being taken in randomly rather than bunched in phase groups.
As said above there will always be induced currents from singles but it is much worse if they pass through ferrous metal. In another case we had four singles passing through a steel plate, again there was signs of heating. This was solved by cutting a slot to link the four holes (which were in a line) then brazing it shut again to retain strength. The brass in the brazed joint was enough to prevent further eddy current damage.