The reason I feel like we shouldn't use both Big Guns and Scour in a 3 round event is because they're basically identical.
They're identical in mechanics, they are
not at all identical in how they play out. Mostly because armies tend to favor either heavies or fast attack, and partly because heavies and fast attack usually behave completely differently (Fast attack being, y'know, fast). In any case, if you do only big guns you're being good to say, Tau and GK players but mean to Tyranid players. Scouring is going to be good for say, certain Neron and DE builds, and bike marines, but horrible for Tau and lots of other armies. Only a few armies are likely to bring some of each.
I do not feel the 6 objectives is the essential element of either mission. I would feel free to drop that down to 5 and align it wiht a more standard Objectives mission. Have the primary be only the objectives scored with troops, the secondary only the objectives scored with whatever special we're doing. You could even do it with Emerporer's will.
The fortifications thing is only an issue with the Bastion, right? The defense line we've concluded must be forfeit except for maybe the gun, which may or may not be significant enough to force a change. I'd like to get this worked out and feel correct though.
No, I don't think so? Very seriously, this all goes away if you just count what is killed, which is how the Victory Points is supposed to work, anyway. Yes, it means Aegis players have 50 pts that cannot killed....really not the biggest deal. Bastion's count when they are killed, as per normal, regardless of who posses it. If you want you can also give up VP if the enemy actually occupy's the thing, but that is nearly impossible unless the owner "gives it up" without destroying it, so it's really just for funnsies.
I don't know if I love the Relic mission being primary. I feel like it does favor / force armies to move, which is good. I just don't know if I'm okay with that after moving to 3 Relics. The strong get stronger type of thing. Maybe this matters, maybe this doesn't. Personally, I really like the way mission 3 looks as it is, but I'm open to suggestions.
Relic, and all "push" missions (like, when the obj on their side are worth more than yours) inherently favor some types of armies: high mobility, and slower mobile durability, i.e. it hurts gunlines. Meh? THat's something GW has decided it wants to do, and most of us seem to want to do it to, since a lot of custom missions have that kind of design. I do not see how 3 relics punish it any more than one. Really, I'm not sure I understand the nature of this particular objection. I do think Relic should be primary for one, it's the only truly New 6th ed mission.