All I can say is that I am 2 years post bypass. I lost 100% of my excess weight in 7 months, am keeping it off, and am not deficient in vitamins or minerals. The restriction is much less now than it was a year ago. I focus on whole, plant based foods which allow a tremendous amount of volume. I can eat basically as much as I want, and control weight by monitoring the grains, nuts, nut butters, and seeds. Those are the most caloric dense foods I eat, and it is easy to tweak caloric intake up or down by adjusting those.
I think the people you know who have had bypass and are vitamin deficient are the exception to the rule. Are they taking their supplements? The malabsorption part of bypass gradually goes away, but bypassers are still supposed to be taking their vitamins unless directed otherwise. You do not see all the other bypassers out there who are doing fine, look great, and are not deficient.
I had bad GERD, so bypass was my only real option. But I would have chosen it anyway. This is major surgery and I only wanted to do it once, and get all the weight off once and for all.