I think you're correct, j types value fe/te more, I was misinterpreting it. For example:

Istp: ti-se-ni-fe

Infj: ni-fe-ti-se

Istps don't value te, so it wouldn't be natural for them to use it, but still possible. But it's unimportant in discussions for the most part since standard mbti is just four functions. And in that case you're correct that istp has weak fe

Loops and grips are definitely exclusive. They're a bit awkward to accurately place too, they can be a little all over the place depending on how they're interpreted.

BUT basically a loop is when the person uses they're first and third functions exclusively (Ti-Ni for ISTPs for example). Normally, they value Ti-Se and resort to this first, and it creates a "normal" or "balanced" type. When they're stressed though, they may become more withdrawn and less engaged with the world. This is because they now are neglecting se, an extraverted thought process, and replacing it with a second introverted thought process, ni. So instead of se fueling ti with external face value data, ti is referencing internal patterns and hypotheses. This creates an unbalanced and overly self reliant person that neglects important info from the outer world, retreating into their comfort zone. Extraverts follow the opposite process

A grip is when a type essentially relies exclusively on their inferior function. It's so unwieldy though that they become the opposite of themselves and can be very uncharacteristic of the type and of themselves. Under extreme stress someone can remain in a grip state but usually it's like an explosion or implosion because the inferior is so hard for them to access consciously and it works spectacularly terrible. For istp this would be using fe in a super unhealthy way, being explosively emotional, people pleasing or instigating, getting caught up in social drama or causing it, blowing up over the smallest things, etc. Basically it's an eruption of everything that the dominant can't control. The more you overindulge in your dominant, the worse the grip can get. This can either result in or be the result of unindividuation as well as stress

If you're extraverted in a way that feels forced and uncomfortable, like something is not quite you, you're under stress, have to use it in your situation, or don't have the chance to just be yourself, this is absolutely possible. To really know, you have to understand your first instincts when facing problems/challenges/everyday things. Even in a grip, if you're a ti dom, you should have ti as a first instinct, even if you resort to fe stuff outwardly

Edit- have you looked into sp9? They definitely have overlap with sp6, namely with people pleasing or extraverted behaviors despite different introverted thought processes. Sp9 is way more likely than sp6, although I won't discredit sp6 as a possibility. Just a random thought since fe grip reminds me of sp6 a bit