Don't know about pool pumps exactly, but blanket claims about magically better efficiency might well be true. The problem isn't fixedness, it's usage of poor efficiency motor types. We saw this in hydronic heating loop circulation pumps: the older types consumed 70W at maximum speed, and the replacement variable frequency types (don't know if they are internally BLDC or what) consume like 20-25W at the same flow rate and pressure. The difference grows even bigger at reduced flow rates. The old type is simply a cost-optimized capacitor-run single phase AC induction motor with a lot of slip. It's same as with fan motors: a 10-15W BLDC "computer fan" produces same pressure / air flow as a 50W mains fan.
To answer your question, you should not start from the specifications of the new variable speed pump, but instead try to find out what is the efficiency of your current fixed speed pump.
Remember that in circulation systems the physical work to lift water is zero, and you can consider the whole power consumption as losses - friction and electric. Therefore, it is entirely possible, and not even difficult, to get to very low consumption. To me your numbers sound high. If the current pump is of inefficient type, replacing it would be the first step. The next step would be to reduce mechanical losses, probably by first increasing the filter area. If that is not sufficient, pipes can be replaced by larger diameter size.
There is also synergy in doing these steps. Say, you decrease pressure drop of the filter by making it larger, halving mechanical losses. But the old fixed-speed pump has a narrow efficiency sweet spot, so power consumption does not drop to half. Add a VFD pump (and the point here is not the speed, it's the commutation strategy), and it will have much wider sweet operating region. It's like comparing switch mode supplies where one does have pulse skipping and other does not, in light load conditions.