I think the author of that post had a lot of astute observations about the differences between the two types, but I disagree with the bolded:
INFPs are the opposite, they have well developed philosophies on everything and readily go into in depth verbal discussion about things but specific things they see in shades of grey and therefore lack the raw gut force of the ISFP. This is often shown in the face of a threatening opponent- INFPs often balk in this situations whereas ISFP can go badass fuckyou die evildoer mode.
Overall, I don’t think either IxFP is generally more confrontational or aggressive against perceived enemies. IMO both types are equally prone to Te bitchslap mode if pushed far enough, and when an INFP gets to this point they will put aside analyzing the situation and trying to consider all the nuances, instead directly taking action in response to some violation.
I think enneagram type and individual temperament have more to do with it than Ne/Si vs. Se/Ni, with e4s (especially sx-dom) and e6s being more likely to go into “fight†mode against someone who crosses their values compared to 9w1s, who tend to be the more passive IxFPs and generally have more trouble acting on their anger even when they’re intensely aware of it. Healthier 9w1s can stand up for themselves and confront others when necessary, but even then it usually lacks the "die evildoer" intensity the author mentions. IMO 9w8s and e5s are usually in the middle. And like I said, a lot of it just comes down to individual differences in disposition and tendencies that aren’t related to type.
NFP/STJs love MODERATION, they like balance, taking things to the center. To them the key to life is doing everything, but not too much. They dont have any overwhelming energy directed in one specific direction.
I think there’s some truth to this, with Ne-users often having broader interests and enjoying exploration of many different ideas and pursuits, while Ni-users tend to be narrower but more focused in their interests and pursuits. Also, Si-users often have less of a craving for physical adventure and intense sensory experience so they’re more prone to living physically moderate lifestyles.
However, I think enneagram instinct stacking influences this too -- I would expect those with a strong sx instinct to be less moderate and balanced in the way this person describes, and instead to be the ones most likely to have much of their energy intensely concentrated and directed towards one or a few areas in their lives.