FF14 is not made for hardcore players.

[linayar]

Sure, but the opposite is also true where many players appear to assume advice = opinion.

For example, they receive constructive criticism that can be backed up with math, logic and reliable sources but don't even listen in the first place because "that's just their opinion and I prefer mine", and continue on their way playing Ice Mage, single pulling mobs or spamming Cure I all dungeon.

So, just to be clear here, the opinion in your scenario is not the math that may certainly say certain playstyles are not as efficient. The opinion is that, therefore, those playstyles should not be used even on content that would still be clearable with those playstyles.

On the other hand, it doesn't really matter if an advice comes with an opinion. If you genuinely think it's good advice, then you should give it unless you're corrected in that it's not a good advice after all. But the other person can still choose not to take the advice regardless.

[Veis_Alveare]

But the other person can still choose not to take the advice regardless.

And if they do so they're being the toxic ones, wasting other people's time.