I think more important than yield in low interest rate environments is that dividends are generally pretty reliable, as opposed to price appreciation, which is not. A long history of increasing dividends shows a strong underlying business model and history of execution. Furthermore, for mature companies, there is only so much money you can productively employ; retaining money that you cannot use effectively reduces shareholder returns. Conversely, you shouldn't be paying dividends if you are entering an Amazon winner-take-all market because you need it to grow. So you really should care about dividends.
Though maybe the authors know what they're doing and were under pressure to publish (publish or perish in effect?) so they just picked one of the more BS low-hanging fruit theorems in economics to poke holes in for the millionth time.
I don't think its totally irrelevant. It may not be applicable in a today's real world, as you point out. But the point of a model is to try to explain what happens when you change the input parameters.