As I understand your question, you are looking for a less challenging route from Indiana to the East Coast.
The Northern Tier route gets "challenging" after you leave the Erie Canal tow path and heads up into the Adirondacks. Then comes the Green Mountains of Vermont and the White Mountains of New Hampshire. Finally, western Maine has some good hills that don't really show up on the profile.
So, alternatives to the Northern Tier would include continuing on the Erie Canal to Albany, and then either going down the Hudson to NYC or pick up Route 20 towards Boston. You will need to cross the Berkshires on this one, but not nearly as tough as Vermont and New Hampshire.
Another alternative would be to pick up the rail trail linking Pittsburg and Washington DC.
I have done the Northern Tier, I haven't done route 20 in total, and did bike the C&O many years ago.