How prevalent/popular was 4N 2-3 years ago, assuming tapeout was determined around 2021-22.
4N didn't exist till 2022. It's a customized process specifically for Nvidia's use, and it debuted with RTX 4090 in October of 2022.
The 5nm node that it is based on had it's first products roll out in October 2020, starting with the newest (at the time) iPhones. In general, high end phones and GPUs move to new process nodes first, because the early customers for those products will pay huge prices, which compensates for how buggy the initial launch of a new node often is.
For a modern portable device, the node basically
never exists before the chip does. There are subnodes and micro-updates to existing processes. And for devices which don't need the most advanced node, you don't
design for an older node. Instead, you just use an older chip that was designed for a then-top-of-the-line node that has become cheap. That whole process helps subsidize the cost of these annual, high-cost chip designs.
There is no other product that fits into the Switch's niche, so there is no
"normal" here. Tablets don't have a 7 year shelf life like a console, certainly not while targeting a launch price sub-500 USD. They don't have chips that are never destined for other products, they're not built for GPU performance first.
But consoles aren't built around tight battery, heating, and space requirements. They don't start with size and power draw and work backwards to performance. And for Sony and Microsoft, they're not built to be profitable! They're built to entice folks away from the other guy, so that they can make money on software sales.
One of the reasons we've gone in circles so many times on this is because you can't clearly look at existing examples to get a feel for the likely moves by Nintendo.