Myron, W0PBV wrote:
"Is that low efficiency of 30-50% really true?"

No. The pi network would not be so popular were that true.

The efficiency of a Class B or Class C amplifier is higher than that and
the network by itself is very low loss. RF amplifiers typically have
efficiencies well above 50% because much of their source resistance is
of the lossless variety.

Search the internet for: "pi network antenna tuner". One entry near the
top of the list is from Collins for its 180S-1 Antenna Tuner. It is
basically a 1000 watt "pi" network for matching various antenna
impedances to a 50 ohm coaxial transmission line in the range of 3-30
MHz. In most cases it is used as an "L" network, but when the "L"
network cannot match the desired antenna, the complete "pi" circuit is
used. The vacuum variable capacitor employed in the output circuit can
be connected either in series or shunt with the antenna. The 180S-1 is
useful for tuning trailing wires on large aircraft.

Ralph Hanna, W8QUR had it wrong when saying "The big disadvantage of
this system is the low efficiency."

Best regards, Richard Harrison, KB5WZI