The transition from animal power to mechanized vehicles was a much larger shift in innovation than ICE -> BEV.
Is it? Doesn't seem obviously so to me. How about going through your rationale?
Be sure to keep in mind the "refuel at home" equivalence for animal power and BEVs, etc.
Horses are living creatures that require effort to keep alive even when not in use. As living creatures they're limited to a daily range of 10-20 miles, depending on load and conditions. Automobiles don't have any of these limitations, but are a lot more technologically sophisticated. A horse drawn buggy is relatively simple to create and assemble, which was typically created by a craftsman. Whereas the automobile required thousands of moving parts, specialized engineering, factories, and assembly lines.
Other than the drive-train, the manufacturing process for BEV and ICE vehicles is more-or-less the same. Suspension, body, seats, interior, etc. An ICE drive-train has around 2000+ moving parts, whereas a BEV has around 20, so the complexity of the BEV supply chain and manufacturing process is actually lower, which means a lower barrier to entry for competitors.
I'm not a legacy fanboy, but neither am I a Tesla fanboy. It's worth noting that legacy makers aren't the only competition, as Rivian and others also enter the fray. I simply don't buy the narrative that Tesla is SO far ahead of the competition that other manufactures cannot catch up. The Mach E is a darn good EV, especially for Ford's first iteration. The legacy companies are already ramping up, not yet to Tesla's level, but I believe they will get there relatively soon.