Imagine, you make a game accommodating various playing styles. And then you outsource bosses to some studio who only knows how to make things go boom.
http://www.gameranx.com/updates/id/2963/article/deus-ex-human-revolution-s-terrible-boss-fights-were-outsourced/

It's all coming together.

It makes sense, but it doesn't excuse. There was a failure somewhere in the process, either in feedback or management that they still ended up in the game as they did.

I honestly can't understand why would anyone outsource boss fights in a game to a completely different company. It's such a ridiculous idea you have to wonder what sort of a tie-wearing clown is it who makes these decisions. Not to mention it couldn't have been cheap, either.

Weak excuse. I presume specifications were given when outsourcing and there's no way the result doesn't fit those specifications at least in a broad sense. It's pathetic to try and throw blame on someone else for their design choices.

Whatever. Sucks a bit on the first playthough since you don't know exactly what's what, but on the second they were no that difficult even on hard.

I have never played the game so I wont argue right or wrong with you, but to address your question on why... Its a timing choice. There are limited resources to go around and usually outsourcing does two things, saves you cash in the short term (sometimes even the long run depending on the dev job market) and allows your in-house resources to address more pressing issues. Second, it allows you to make your fabricated dates.

In this case they simply may have assumed that the boss engagements where formulaic enough that anyone could do them and they would be the most effective thing to farm out. In essence they are right. Boss fights are pretty self contained for most games. Again, never played it myself, but in theory this should have been a pretty safe bet. Apparently they just busted out.

I haven't played the game either, but common sense tells me that if you don't have the time or the resources to include a non-vital feature, you just throw it out. It's not like the game wouldn't work without the boss fights -- pretty much every single reaction I've read says the exact opposite, actually.

Imagine 20 years from now the developers of Civilization 10 admitting they outsourced the combat to a hentai dating sim studio.

Game of the year right there, IMO.