In general the Major Resolve skills are a staple of every PvP build. I don't even think about not slotting them, so it's interesting you should question this.

One reason those skills are used by every class is that they all offer something in addition to Major Resolve. DK gets extra healing from a passive. Templar gets resources. Stamsorc gets AOE damage, NB detection and speed. And so on. For warden it's Minor Protection and group utility. Now that I think of it, you could indeed argue that this is one of the weaker skills in the group. You do get the Minor Protection on your other bar, though.

The short answer is, if you are running light armor and have only around 10K unbuffed resistances, you might arguably forego Major Resolve, even though I have never tried. This is because armor penetration is pretty meta and, if your opponent has 15K penetration, it does not matter whether you have 10K resistances or 15K. You will be fully penetrated (ugh) and take full damage either way. However, if you have 20K upwards of total armor (with buff), then you tend to feel every little bit extra. On the other hand your opponent may not be specced heavily into penetration, but into weapon / spell damage or crit. In that case the Major Resolve buff is even useful on an overall low resistance build. The conventional wisdom is to run it.

If you have 33K effective armor, you mitigate 50% of damage. Since this is offset by penetration in PvP, you would need around 45K armor to reach 33K effective armor under realistic conditions, e.g. against a player who has 12K penetration. You can't really have enough resistances.

An important thing to note is that armor, up to the 33K cap, is additive. If you take the Major Resolve buff, this really does tend to give you 8% damage reduction and this is something you will feel. You tend to feel it more, if you already have high resistances, because all of the Major Resolve buff will be above your opponents penetration value. You also tend to feel it more, because armor is the single biggest damage mitigation factor other than blocking and Mist Form.

Buffs, other than armor, are multiplicative. Let's say you have 20K armor, giving you 30% mitigation and you stack that with Minor Protection. The way this is calcuated is:

Damage taken = 0.7 (70% damage remains after armor) * 0.95 (95% damage remains after Minor Protection) = 66.5%.

NOT 65%. Buffs like Minor Protection are multiplicative. If you have armor to the tune of 30% damage reduction, then Minor Protection only adds 3.5% further reduction, not 5% like Brrrofski said. Extra armor, however, is ADDITIVE with the armor you already have. Where your choice, for the sake of the argument, is between adding extra armor to the tune of 8% damage reduction or some other buff that, on paper, also gives 8%, extra armor will give you more in practice. It's actually a little more complicated - neither armor nor the other buff will give you 8%, if you have multiple mitigation factors - however armor tends to be your single biggest mitigation factor and adding to it tends to reap the greatest rewards. Paradoxically also: Stacking armor on a character that already has a lot of it tends to feel more effective than shoring up a low-armored character - the reason light armor may feel squishy (to some extent) regardless of what you do.

There are some things I am not certain of. I never checked how the damage calculation for buffs, like Minor Protection, works when armor is partially penetrated, as it always is in PvP. Does that recoup some of Minor Protection's effectiveness, because your effective armor is typically much lower than the armor on your stat-sheet? It probably does.

Major Resolve is a must. Dump the psijic order ult. Use something else and use Icy Fortress

You have the option of using the other, cheaper morph and forgoing the minor protection, the cost is about 33% less IIRC. If it's a choice between maj. resolve with minor prot., versus not using it at all, then this might be a good compromise. Plus if you already slot Temporal Guard then you're only losing minor prot. on your front bar.