definition and usage for whipsaw?

Your reference gives a premodifier usage it wrongly terms adjectival, but which is certainly relevant.

Here are two examples of the premodifier usage given at the Merriam-Webster entry for 'whipsaw' (though it does not give the recent metaphorical sense for the noun):

1. The whipsaw nature of the state’s regulations ... [Scott Wilson, Washington Post, "California reverses reopening as coronavirus cases spike," 30 June 2020]
2. The whipsaw action came just one day after a historic rout that saw the blue-chip index drop by 2,013 points, the most ever. NBC News, "Stock markets rally, with Dow surging 1,000 points at closing bell," 10 Mar. 2020]

The metaphorical premodifier usage is now common currency.

And further recent examples collected by M-W:

3. One described the effect as a whipsaw, saying the company and union would try to convince workers to accept a bad deal or see jobs shipped away. [Eric D. Lawrence, Detroit Free Press... 16 Nov. 2019]
4. The president’s rhetorical whipsaw came against the backdrop of tense but cordial meetings in Biarritz, France. [Michael D. Shear, New York Times ... 25 Aug. 2019]
5. The whipsaw of weather and market forces make for long seasons of uncertainty.[Autumn Schoolman, Indianapolis Star, ... 4 Feb. 2020]

show that the metaphorical pure noun usage is also gaining currency. Also, the 'president' example shows that there is a broadening from the 'dilemma' problem sense or 'involving successive ups and downs' problem sense to the 'speech highlighting the dilemma' or 'speech involving a series of U-turns') senses, one of which you ask about. However, 'rhetorical whipsaw' is probably less jarring than a plain 'whipsaw' would be here.

I'd be careful about using the bare noun as a metaphor for a whipsaw/dilemma-related speech or argument. Especially when there is more than one unbroadened metaphorical usage of 'whipsaw'.

The nounal usages correspond exactly to the verbal counterparts:

[A] whipsaw: to beset or victimize in two opposite ways at once, by a two-phase operation, or by the collusive action of two opponents

• wage earners were whipsawed by inflation and high taxes

[Merriam-Webster]

[B] whipsaw: ... To [move or] cause to move or alternate rapidly in contrasting directions: The bond market ... continues to be whipsawed by fears of rekindled inflation (Steven E. Levingston).

[AHD]

So is "He delivered a whipsaw [lecture]" a lecture about a two-pronged assault we need to counter, or one full of U-turns? I'm not even sure which senses are intended in most of examples 1-5 above.