Thanks for making this guide! Here are some of my thoughts and opinions about the skills in your team build based on my experiences using 7-hero teams to clear hard content: DoA, UW, hard mode EotN dungeons, etc. I'm not expecting you to drop everything and change your builds based only on my feedback, but more discussion can't hurt!
ST Rit
I prefer Signet of Creation over Boon of Creation for ST prot heroes as energy management. Boon makes the hero lag behind the party a lot of the time due to the 2s casting time and if they recast it mid-combat, you've lost most of any energy savings you might have had. It's also one of the few enchantments on your team, making it likely to be stripped in a lot of cases anyway.
I'm not a fan of the low level Splinter Weapon. The skill is amazing at level 16, but at 10 I don't think it's worth splitting your stats over. I'd rather use a couple slots on my ST prot for monk-based hex removal (and swap the Shatter Hexes to something more generally useful).
Mesmers
I've found Hex Eater Signet and Shatter Hex to be poor primary hex removal skills. Touch skills effectively add 1-2s to their casting time as the hero spends time running around and the hero AI does not use Shatter to prevent the effect of hexes, only when it will deal damage to the enemy, which can matter if you are not melee. Additionally, shatter costs 10e, which drains more of your resources than necessary if you just swapped in a couple monk-based hex clearing skills in their place.
I also think half-cast portion of 40/40 sets don't add much to your dps when you're hitting 13+ FC since at that level you're spending more time in after-cast animation (locked at 3/4s) than actually casting your spells, at least with hero AI being what it is. I prefer running Insightful Staves of Fortitude (inscr can be "Apt not Att" to keep some casting time reduction or "Hale and Hearty" to boost energy even more) to help limit the burden on your BiP battery. The generic recharge reduction will also work on any secondary Inspiration or Illusion skills on the bars, which is a nice benefit.
I prefer Signet of Return over FoMF as a hard res because while the res target ends up revived at roughly the same HP either way, the signet has no energy cost nor drains HP from the caster. There are obviously situations where FoMF will work better, but SoR is a viable alternative.
Minion Master
I'd really like to fit Stand Your Ground in here as a option for players not running Save Yourselves. Boosting your party's armor by +24 is really good and you've got the attributes and energy for it.
B-Surge Ele
I'd recommend offering Thunderclap as a variant elite for caster heavy missions/dungeons/zones. Not getting to take advantage of the 40/40 air set most of the time due to Protective was Kaolai makes me sad, but I'm not sure what the alternative is.
Invoke Lightning alternate for MM
I'd recommend a Ray of Justice monk in this slot (at the very least as an option) since many of the areas where a MM is bad are filled with undead that make smiting monks great. RoJ monks may be a tier behind E-Surge, but I think they're still effective heroes.
If you're set on keeping an ele, I think I'd rather have Thunderclap + Chain Lightning for hybrid disruption and damage or Elemental Attunement Fire Magic for pure damage over Invoke, at least since the changes to overcast on these skills.
Margrid
I get that rangers are not top tier heroes, but they can dish out some strong single target DPS with Enraged Lunge or Strike as One builds that should be better than a random assortment of mes interrupts.