Actually, no. Replicating the manual process was quite feasible.
There were keyboard-driven typesetters that worked well. Here's the Unitype.[1] This sets type by assembling type slugs into a line. It doesn't cast hot metal. It even has an automatic distribution system; it can sort type slugs by letter, so you can reuse the type. That's the same thing the Paige machine did. The Unitype was much simpler.
The Unitype was late to market. Mergenthaler already had the Linotype out when the Unitype shipped. The Unitype was half the price of a Linotype. Unitype machines sold for about 20 years, so it wasn't a total failure. The Paige machine uses a lot more parts and space to do the same job.
Mechanism design skill is very rare. All the good Teletype machines were designed by just two people - Howard Krum and Edward Kleinschmidt. There were competing machines, and they were all much worse. William Burroughs invented the first adding machine that worked reliably, and it was better than all the competitors. Burroughs dominated banking well into the computer era.
The video claims that the big problem with the Unitype that it required not just a keyboard operator, but someone manually justifying the lines at the output end. Linotype figured out automatic justification, using expanding wedges. No need for a second worker.
Plus someone had to feed used type back into the Unitype for sorting and return to inventory. With a Linotype, the matrices with the letter forms never leave the machine; they are dispensed, set into a line, used for casting, and then immediately recycled back to the magazine for further use. As long as the supply of lead bars ready to melt holds up, you can keep setting type. With ordinary type setting, mechanized or not, you can end up with all your type tied up in pages waiting to be printed.
So the real problem with the Unitype was that it wasn't labor-saving enough.
Despite that, it powered many small country newspapers for years.
[1] https://youtu.be/5n5JQrN8qx4?t=152