What are the odds the ABS pump finds itself in a situation where that sort of bleed is necessary in the first place? I would think the innards would hold that fluid in even if you empty the master cylinder? If that's the case, the real point of a tech2 type bleed would be to purge that old nasty fluid out.
ANY vehicle with poor brake hydraulic action needs the ABS bled, if equipped.
And, yes, when I "bleed" brakes, what I'm really doing is a brake-fluid flush. I don't stop until it's virgin-clear at every bleeder screw. I even clean the reservoir.
To be honest I have been fighting the squishy brake issue on my '88 Supra as well. It has ABS as well, OLD SCHOOL, and it's an OBDI car. There was a dealer only special service module that connects to the abs unit itself to activate it, but other than the rare unicorn that appears on ebay for WAY too much money they basically don't exist. I have attempted multiple times to do the whole activate the ABS multiple times then bleed it... I've tried the dance of making the ABS module the highest part of the car then bleeding, cracking open the lines at the moduel... a number of different things and none of it has worked. Kind of an aside, but I am at a point where I'm working with some old forum data to try and reverse-engineer the dealer control module, and ABS wiring, to build my own "service tool" to activate the ABS and actually get it bled. At this point the fluid is crystal clear in the car and it still has soft brakes.
SO-
I'm going to get my hands on one of these cheap bi-directional tools off Amazon and hopefully solve this issue, rather than fight it. The tool I found on this board linked by another member is $113 right now, and worth a shot, I think. Worst case I can't get it to work and I return it.
amazon.com/gp/product/B07CSMJJK9/ref=ox_sc_act_title_1?smid=A2YWURTSRUAKKQ&psc=1
I definitely need to pull the drums off and have a looky and at least clean up and grease the contacts, as mentioned earlier. I have new front brake pads already... I'll probably also replace all the rubber lines.
But I'm completely convinced now 90% of my issue is air in the system. AND my old '98 2500 suburban had squishy brakes as well, you had to bury the pedal to get them to work. Definitely had the same issue. Very frustrating...