Cottered chainsets, which cover most solid steel chainsets, are are the work of Satan. The pins often either work loose on the road, or are seized when you need to service the BB. With careful fitting, these problems are minimised but few people or bike shops have a cotter press nowadays, or can be bothered to file pins for the optimum fit.
Solid steel cranks are plenty stiff enough but weigh a ton. Ashtabula one-piece cranks avoid the cotter pin problem, but the BBs are badly sealed and they are even heavier.
Some very good hollow steel chainsets have been made, e.g. Tioga Revolver and Cook Bros (for MTBs). These weren't cottered.