I know the previous GM sucked but they did expend a lot of draft capital on the OL.
We know 3rd through 5th round picks on an interior linemen is considered relatively high. These players rarely get picked with premium picks. Look around the NFL, most are mid-rounders with plenty of UDFAs even playing.
But you can easily look up what they did to shore up the OL in Indy:
1st Rounder Ryan Kelly
1st Rounder Quenton Nelson
2nd Rounder Jack Mewhort
2nd Rounder Braden Smith
2nd Rounder Hugh Thornton
3rd Rounder LeRaven Clark
4th Rounder Zach Banner
4th Rounder Khaled Holmes
5th Rounder Joe Haeg
6th Rounder Justin Anderson
7th Rounder Austin Blythe
7th Rounder Denzelle Good
The above numbers also leave out the fact that they drafted Castonzo in the 1st round the year prior to Luck and he was the left tackle all along.
They also brought in starting FAs like Satele, Cherilus, Donald Thomas, Herremans, Slauson.
The Colts have actually expended more draft capital than most teams on their OL. There are plenty of starting late rounders around the league, UDFAs even. Last year the Patriots, for instance, had this: 7th rounder, 5th rounder, 4th rounder, 3rd rounder, UDFA. This isn't uncommon.
Usually interior lineman go 3-7 rounds, tackles are the premium players.
And not all of those OL were busts either.
The Donald Thomas story is an interesting part of this. He has a pretty good season with the Patriots, then signs a big contract with the Colts, he loses his starting spot, then comes in and gets injured, and that was basically his career.
Luck really held the ball too long and did not have much regard for his body. He was tough pain-wise, but fragile. Willing to put his body on the line, but look where it got him. As I always say to the Bills fans at the annual Patriots game in Buffalo, when they start chanting, "Brady is Lady" (the women are chanting too), "How is it that the most effeminate QB in the NFL is also the greatest QB in NFL history?"