IMHO methinks you're being a bit harsh on the so-called "house blends".
I guess to most of us here, the entry-level whiskies like Jim Beam (White Label), Jack Daniels, Canadian Club, Ballantines, Bells, etc, etc, are a bit dull on the palate. But I doubt very much that their producers make the spirit with a view to it needing to be mixed to make it palatable!
The reality is that the vast majority of people find straight whisky too strong or unpleasant, but they don't mind it when mixed. I know a few people who happily shell out for better quality whiskies, (JW Black, even a few single malts) and still mix it with coke because that's how they enjoy their whisky.
But I doubt very much that the master blenders concoct their recipes and then add coke & other mixers to find out if they've hit the winning formula!!
I guess at the end of the day, one man's poorly made whisky is another man's elixir.
Many standard blends are marketed to be used with mixers because they want younger people to take them in their hand. This then will be a market for years to come. Then they can "progress" onto more sophisticated/more expensive whiskies if they want.
I'm sure the manufacturers don't care how anybody drinks their whisky as long as they drink their whisky.