I did a lot of work with 4-10MHz equipment quite a number of years ago, and it did work well. A number of them required external RAM and external EPROM, consuming lots of power and making lots of external signals jump synchronously.

It should still be possible to use solderless breadboards now - people have a choice to decide how high-impedance they want their signals. And lots of microcontrollers have internal RC oscillator good enough for normal UART use, removing a lot of needs for an external crystal.

Professional developers always looks down on people playing with these solderless breadboards. In reality, quite a lot of engineers got their initial training using them.

It is obviously a lot better to use soldered prototypes. And since I can afford it, I don't need to think about component reuse. But that is not the situation for many beginners. Especially since their initial designs may change a lot because of trial-and-error designs.

An important issue is that beginners have just as big reasons to play with blinking LEDs now as they had 15 years ago. Not everything are designs that runs the ADC at 100kHz or runs 5Mbps SPI links or processes 10ns pulses. That solderless breadboard do teach people why debouncing is needed the hard way. A skill that is valuable to have.

Of course, beginners today have the advantage that they don't need to start with raw chips. They can get cheap development kits and just use their breadboards for I/O designs. But remember that without a digital scope, lots of people starts with projects where the signal speeds aren't higher that they look at signals with a LED or a DMM. And where the speed difference between bounces and real signals are so huge that it's very easy to debounce the signals.