Maybe I'm misunderstanding, but I wouldn't expect "Sugar Babies" to be looking for potential husbands on those online platforms. Whereas mail order brides seem to be in for a longer commitment.
If the two value propositions are so different (essentially a hot temporary girlfriend vs a wife), there is no real competition, and the bargaining power should not be too affected.
For the mail-order brides who actually want to be someone's bride, yes, it's a bit different.
That certainly doesn't seem to be what the article describes and it's hard to see why Western men who were strangers to the women would agree to this arrangement unless they were being paid.
Also, having gone through the process of getting a green card for a spouse, I think this would be harder than you're probably imagining.
Look at a "regular" dating site: there are far more active male users than female, the men send almost all the messages, and the women reply to nearly none of them.
Now look at one of these mail-order bride "dating" sites, or, equivalently, a "sugar-baby" site like SeekingArrangement—where, in either case, the men come pre-qualified as having money and being willing to give that money to the women: now, on these sites, there are far more active female users than male, the women send almost all the messages, and the men reply to nearly none of them.
When you take non-wealthy men out of the dating pool, suddenly there are few enough men left that supply-and-demand forces women to compete over men. Which puts them in a much weaker negotiating position than they would be otherwise.