I'll take the franchise player at any position at this point, but the preference is defense because that is a much more important factor to winning championships. As you can see, even if he's surrounded by mediocrity, even a player like Von Miller can change a defense.
The "domino effect" that occurs on the OL, I'm not sure it exists. If you draft Matthews or another OT that high, there is always that expectation, but I don't see much historical precedence to suggest that expectation is real (see Browns or Rams OLs this year). What it usually involves is that you've now solidified 1 spot, and you still have to find better players at the other spots. Maybe if you have a decent guy playing beside him (and we do with Blalock), then you've turned one side of your line from a weakness to a strength. But it still won't affect how the other 3 guys play. They could still suck. The right side of our OL is our most glaring weakness, but the left side is by no means a strength. If Matthews changes that, then it makes it easier for schemes/protections as you can use TE and RB to chip on the right side and be relatively confident that you can leave your left side guys on an island (typically NFL teams roll their protections to the left, which means the RG is on an island rather than the LG).
It really boils down to how the Falcons see their current group of OL. If they think Baker/Holmes competition can suffice at LT, then there's no real reason to take a OT in the Top 10 because the value in drafting a RT that high doesn't really exist unless you're grooming him to replace a soon to be gone legend at LT, and his stint on the RT is only going to be for 1-2 yrs max. IMO, if we're drafting an OT that high, he better be a day 1 starter at LT. And you move Baker/Holmes to right side and hope they fill in. If they don't, then you find some midlevel player to replace them (because again, you don't need to spend huge to get a competent RT).
The real issue the Falcons face is the possibility that Holmes/Baker stick at LT and the fact that if Baker plays like he did in 2012, and Holmes plays like he did for parts of 2013, you have a competent LT. Not a good one, and a guy that will struggle against top competition, but he's not going to be the reason you don't win it all. It's like you're starting the equivalent of Stephen Nicholas there, you know you can do better, but you can live it with for at least the next 2-3 years that they're under contract for. And you'll worry about the upgrade 2-3 years from now when their contracts are up.
But the other possibility is that they suck again. Holmes is just J'Marcus Webb v2.0 and Baker is the s***ty version of Baker that we've seen more often than not over the past 6 years.
So essentially you're in a low reward/high risk scenario, and thus if you're taking an OT, then he better be a rock-solid Jake Long, Joe Thomas, Ryan Clady-esque guy that you feel like is a can't miss guy. If you don't feel like that guy is available in the draft, then there's no point taking him that high. Maybe you trade back 10-15 spots and find an Anthony Castonzo/Riley Reiff/Nate Solder type that you're pegging more to become a serviceable to good starter.
So the point is that if you're going to take an OT that high you need to really believe he's Jake Long/Trent Williams/Matt Kalil i.e. the type of guy that is going to be a Top 10 caliber LT for a long time.
"Vincere scis, Hannibal, victoria uti nescis" -- Maharbal, 216 B.C.E.