Op. Amp instead of Push pull stage as power amplifier
The main power contribution of an emitter follower push-pull amplifier is from its current gain. This can be quite substantial.

Op amps generally have low output current, on the order of 20 mA or so. That most common type are much better suited to voltage amplification.

If you put the two together you can produce large amplification of small signals. The op amp can be used as a preamplifier, to bring a signal of say millivolts up to volts (but milliamps of current), followed by the push/pull stage that keeps the voltage about the same but amplifies the current to produce watts of output.

There is such thing as power op amps intended for use without a separate power stage following them. The LM675 (datasheet here) is one example, but a search on the term "power op amp" will bring up many others.

The closed-loop output impedance of an op amp is generally already quite low, so it's not ruled out strictly for that reason. Rather it's the fact that it "saturates" (i.e. cannot deliver any more current) at a milliamp level and would generally start behaving badly (e.g. increased distortion) if used to drive a low-impedance load.