As someone that makes the odd steel frame I should be defending this… But to be honest other materials are often better for full sus if bothered about weight (which I am to a certain extent).
I’ve only previously felt the need to make one steel full sus, but that was for a very specific application (long wheelbase kiddy seat 20″ back wheel low c of g dad special). Steel and recycling some old frames let me make that very quickly (essential because kids grow fast).
Steel is great for recyclability and reuse – I’m currently making a new work bike using a recycled rear triangle from my last-but-one mtb made 10 yrs ago. A different fork and 3 new tubes gives me a completely different bike for very little work.
But today reading the latest singletrack I did get a full sus idea – a steel copy of the Trek Supercaliber with a “non-CEN” front triangle (I’m 64kg so probably safe) could be awesome and barely heavier than a hardtail. Would be like the twang, compliance and comfort amplified in a really good way. And shock loads almost axial along the top tube would be structurally appropriate for skinny steel tubes.