Sort of, the thing about transistors isn't the efficiency as much as the scalability.
You'd be very hard-pressed to make a modern processor out of vacuum tubes. It would be enormous, tedious to build (couldn't use modern lithography), and also consume tons of power.
Sounds to me like you're saying that Transistors are more efficient than vacuum tubes, both in terms of space and power consumption.
The last generations of vacuum tube processors were the size of large multi-story office buildings and had 50k tubes.
Compare to your smartphone, it would take billions of tubes to duplicate it.
If the same R&D might went into thermionics, we might just have devices of similar scales.
It (or major parts of it at least) could be built by a fully automatic / robotized manufacturing plant. That isn't "tedious". Even for a one of its kind processor that would be much cheaper than the manual way.