Yeah, that's exactly it Jason. None of your points were invalid Velrun, but they were all points of critique, and they were worded in a very short and pointed manner, with no offerings of sympathy or a way forward. It fits most of the criteria of
good constructive feedback, except two, I think. Let's start with the important one. Using the sandwich technique, that is flanking (or "sandwiching", hence the term) constructive feedback between two pieces of positive feedback and/or praise, helps make your post seem a lot friendlier to the recepient of your feedback. So, you know everything else was fine, but Chris (in this example) doesn't know you think that. It helps voicing that part of your opinion out loud, or in this case writing it out, to make the recepient of your constructive criticism more receptive to the criticism. Most humans are hardwired to immediately dismiss opinions that seem purely negative (even if they are constructive), and you can help shift that perspective by also including positive comments.
So, this sandwiching technique (also suggested in the link above, as the first point no less), is exactly what Jason is applying. He starts on a positive note: "I think these look great Chris!", then follows up with the constructive criticism: "If I had to nitpick, I'ld say: ...", and to wrap it up you could then end up on a positive note again, for example: "I hope you can find more fitting art in this style, because these really fit the style of the original borderless Triomes really well." Even if you don't go full sandwich mode, just starting on a positive note can take a bit of the edge off.
Another quality of good feedback is providing a way forward, in other words, giving specific recommendations how to improve. Like I said, your points of constructive criticism were very short, e.g. "Untamed Triome doesn’t look like a Forest." You can distill an opinion as the recepient of the criticism, namely that you think the art should feature a forest, but you can easily write a fuller sentence with some piece of advice on what to actually fix. For example: "Untamed Triome doesn't look like something that produces green mana, I think a more fitting art needs more prominent trees, or even a patch of forest." That gives Chris just that tiny bit more to go on if he agrees with your criticism.
That said, I didn't mean for my post to come off as negative towards you Velrun. I mainly tried to give a bit of counterbalance towards Chris, by pointing out the things I
did like about the artworks you singled out. Sorry if it came off as unnecessarily hostile towards you!