The article linked by you is extremely weak. It is not clear what exactly it wants to say and all its arguments are logically flawed.

It should be obvious for anyone that taking some fish oil capsules is quite unlikely to have by itself any significant health effects, unless by accident it happens to complete exactly what was missing from an otherwise healthy diet.

So the article fights a straw man.

On the other hand, having a correct fatty acid profile of the entire amount of fatty substances that is ingested every day has an overwhelming importance for health, as has been demonstrated by a very large number of cases documented in the medical literature.

This has been confirmed by my personal experience. A few years ago I have been scared by a diagnostic of incipient atherosclerosis. At that time I was eating large quantities of dairy, so saturated fatty acids formed the majority of my daily fat intake. I have made some radical changes in my diet, in order to ensure a correct fatty acid profile, i.e. a minimal proportion of saturated fatty acids and a majority of oleic acid, complemented by small, but appropriate quantities of linoleic acid, long-chain omega-3 fatty acids (DHA+EPA) and liposoluble vitamins. After a year, the symptoms of atherosclerosis have disappeared and also other older cardio-vascular problems have disappeared. Since then, I feel much better than before.

Regarding the part of the article about how to get enough omega-3 acids, that theory is just BS that is based on some kind of flawed vegan philosophy (i.e. automatically ALA from plants => good, DHA+EPA from non-plants => not good) instead of being based on scientific facts and on market prices.

For some people it may be enough to eat plant-based food rich in ALA (alpha linolenic acid), but that is certainly not applicable to anyone. The efficiency of conversion of ALA into DHA and EPA is very low and it varies a lot from human to human. The efficiency is lower for men than for women and it is lower for old people than for young people.

Therefore it may happen to be OK for young women to eat only plant-based food rich in ALA, but for old men it is very likely that they must eat some food rich in DHA+EPA. In theory, with enough money one could pay for a medical study to determine whether one's own body can produce enough long-chain omega-3 fatty acids from ALA, to discover thus whether one can be content with eating plant-based food, without omega-3 supplements. Nevertheless, it is much cheaper and much easier to just take a DHA+EPA supplement, even if it may happen with a rather low probability to be useless.

Even for the people who can produce enough DHA+EPA from ALA, eating large enough quantities of flax seeds, walnuts etc. may be much more expensive than eating a very small amount of fish oil and/or less pleasant. There exists a vegan alternative for fish oil, the Schizochytrium oil (from a fungus-like organism and which is improperly sold as "algae oil"). Even if the price of Schizochytrium oil has decreased by a few times during the recent years, it remains at least 3 to 4 times more expensive than fish oil, which makes it unaffordable for many. However there is hope that its price will continue to decrease until it will become competitive with fish oil.

The cheapest vegetable source of omega-3 acids are the flax seeds. From 1 kg of seeds, a young healthy human might produce 18 grams of long-chain omega-3 fatty acids. Where I live, in Europe, 1 kg of flax seeds is a little more than $5. This results in a price much higher than the price of fish oil and in the same ballpark with Schizochytrium oil. However, because of the uncertainty about the personal conversion factor, one would have to eat a few times more than the minimum, which would raise the price well above that of Schizochytrium oil and one would have to eat a lot of seeds. With other seeds or nuts the price would be much higher.