There are at least a couple differences that aren't just based on the specs (wattage, etc.) of current commercial offerings known to the OP.
One advantage of SDRs is that some SDR setups (Hermes Lite 2, et.al.) allow not only monitoring the final RF output, but also allow the use of computer/DSP pre-distortion to help clean up the signal all the way from or through any added linear/final amplifier(s). This would be much harder to do using a legacy analog transceiver with just a remote front panel.
Another advantage of many SDR setups is that they include a remotely observable panadapter or waterfall display to see if the band is active enough to bother, or where the activity is located within the band. An legacy analog setup would require extra equipment (boxes, cables) to do this. Some SDRs even allow (locally or remotely) monitoring multiple HF bands simultaneously (4 or more band "slices" in the case of some OpenHPSDR systems), if you have a receive antenna system that allows this.