There are different types of insulin (short acting, long acting) and the cheapest version isn't always best for a specific person depending on their individual situation. If you want more information on the structural factors of the unaffordability of insulin this article could help: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8597930/
A box of Fiasp or Levemir insulin costs $477-$560.
The better insulins cost more.
If I give myself the $24.88 WalMart insulin, I can not eat lunch at my regular time and then have to eat in the middle if class. (Assuming I had a high blood sugar reading going into lunch and gave myself R an hour before lunch.)
If I can afford the Fiasp, I can go ahead and eat at my regular time. It's just expensive.
My concern is that I need to live a fairly normal life, and I need to work. If I can not eat lunch at a normal time at work, and if I have to get up every 2 or 3 hours all night long to deal with my diabetes, then I can not work a normal job.
This is not a weird objection. The companies distributing the "expensive insulin" also distribute the affordable insulin, and created the cost disparity. Something strikingly apparent to anyone interacting with insurance companies for any chronic condition.
To be clear, your parent is telling the truth in a very literal sense. However, as always, the devil is in the details.
First of all, this is a pretty recent development. The insulins available for cheap at WalMart used to be significantly worse.
The second bit is that wait, how can it be worse? Well, "insulin" isn't always one thing: there are a variety of brands and ways of synthesizing it. They also have different properties. So there are certain things about this specific insulin that may not be great for a variety of reasons. Type 1 folks (I have less experience with type 2, so I just don't speak on it) that have more money or better insurance tend to use two insulins: a long term one, and a short term one. You take the longer term once per day, and then the shorter acting one on a more "as needed" basis. Of course, everyone's health works differently, and so the exact specifics here are between you and your doctor. Anyway, the point is, that this insulin is short-acting, and so to use it correctly, you have less leeway with time and dosage, and that can be rough. And mistakes can be deadly. Josh Wilkerson is a famous example of this in 2019: the insulin his doctor desired for him was gonna be $1200. He opted for taking this WalMart insulin instead, and made a mistake while taking it, due to the differences between it and his previous insulin. For that, he paid for his life.
The third is, this is still inacessible for various reasons, including money. WalMart is not located everywhere. It still costs money to get to WalMart and back. Also, it's $25 per vial, but that says nothing about other costs too. How many vials do you need for a time period? Depends on the person. And a lot of factors. But let's just spitball one: this bottle has 100 units in it. A starting daily dosage, in my understanding, is like, 0.4-1 units per kilogram of body weight. I weigh about 200 lbs. If we take the low end of that range, that would mean I would need roughly 32 units per day. This means I'm using two and a half vials of this per week, at $80/vial that's $200/week or $10,400/year. It really adds up.
This also doesn't take into account other costs: you're gonna be needing to buy test strips as well, so that you can have some idea of how much you need to take. You're also gonna need to buy needles. These are single use. Oh and don't forget that, while you can buy these needles over the counter with no prescription, pharmacists are able to refuse to sell it to you for any reason, say maybe if they think you're going to be using those needles for other kinds of drugs, so you'd better not be in a bad way when you go into the pharmacy, or risk literally having the medicine that allows you to live with no way to put it into your body.
So yeah, like, don't get me wrong, it's a good thing that they sell it. But people like to act all "mission accomplished" about it, when it's just not that simple.