Bread substitute for wheat allergic

Much of the bitterness in breads made from whole wheat is caused by the phenolic acid and tannins in the bran layer of the wheat. Different varieties of wheat have different levels of those compounds and produce breads with different levels of bitterness. "Traditional" varieties of wheat, such as red wheat, contain high levels of tannins, while hard white spring wheat contains relatively low levels of tannins.

Here is what bakingbusiness.com has to say about this subject:

With whole wheat, taste differences boil down to the tannin content of the bran. These red pigments in hard red wheat carry a bitter flavor. “... Whiter whole-grain varieties typically contain fewer tannins, which results in a less bitter taste,” said Brook Carson, technical product manager, ADM Milling, Shawnee Mission, Kansas. "Differences in taste can also be overcome with added sweetness or with a masking agent."

Based on your question, it sounds likely the Pillsbury Chakki Fresh Atta whole wheat flour you use for making parathas is milled from either hard white spring wheat or a blend of the white wheat with a more traditional variety of wheat resulting in a non-bitter end product.

There is another possible source of bitterness in bread made from whole wheat flour, although it shouldn’t really affect commercially made bread. When whole wheat flour is milled, it includes the oil containing wheat germ, which is different than refined white flour where the wheat germ is removed prior to milling. This oil in the whole wheat flour results in it having a much shorter shelf life than white flour and makes it susceptible to rancidity if not stored properly. Commercial bakeries go through (literally) tons of flour, so their whole wheat flour shouldn't be sitting around long enough to go bad.

I can tell you from first-hand experience, one of the signs whole wheat flour has started to go rancid is an increase in bitterness.

I have found the water roux or tangzhong method effective for 100% whole wheat bread, as it makes the texture less dense, and therefore less crumbly.

Also, you may simply be using too little moisture overall. Now that I'm baking bread for a 2 year old, whose tastes lean slightly less rustic in bread than mine, I've rediscovered high-hydration loaves, which, when baked at a lower temperature than my beloved crusty, chewy breads, are pretty suitable sandwich material.

Another strategy, if you want to embrace the density of whole grain breads instead of avoiding it, is to try the strategy employed by dense German multigrain or pumpernickel loaves, which often employ moist sweeteners (honey, molasses or sugar beet syrup), sometimes additional moist ingredients (apples, carrots) along with various nuts and seeds that offset the grains, sometimes alternate grains like rye or spelt, and moderately high hydration. A picture of one example can be seen here: http://www.chefkoch.de/rezepte/1168871222955627/Apfel-Karotten-Mehrkornbrot.html. Then you get a fairly chewy but reasonably topping-friendly bread. (Most German sandwiches using this type of bread are remarkably minimalist in comparison to contemporary American preferences, sometimes meant just as a take-along "second breakfast", and may only have a slice of cheese or salami, some butter and mustard on thin slices). The combination of factors makes for a moister-than-you'd-expect, less-crumbly-than-just-grain, dense bread.