I'd say yes and no. I find very few parts that are custom shapes for a single set these days. Most part shapes are very generic, but there is an absolutely wild variety of them now. There is an enormous number of SNOT, tile and slope pieces, for example. These can make slick looking builds, but getting a decent and useful collection of those for MOCs is hard.
Where Lego gets tricky is the combination of shape and color: the color palette has been growing over the years, too, but most of the weirder shapes are only available in specific colors and not always the colors you would intuitively expect them to have. I guess it happens because manufacturing/stockpiling the whole outer product of shape x color is just infeasible at this point. So the available colors are just whatever is used in the current sets, however weird it may seem.
Where Lego gets tricky is the combination of shape and color: the color palette has been growing over the years, too, but most of the weirder shapes are only available in specific colors and not always the colors you would intuitively expect them to have. I guess it happens because manufacturing/stockpiling the whole outer product of shape x color is just infeasible at this point. So the available colors are just whatever is used in the current sets, however weird it may seem.