"Many players complain and have complained that even investigation missions are too hard to complete, as they are the smartest way of starting a new character that is therefore what I did - Please see tips for new players for other tips. 

Would you please clarify what was exploited? - Making smart gear choices along with weapon selection in order to make life easier is exactly what I needed in order to prove that game is not broken nor impossible to beat."

Those a two "tools" to reduce difficulty that are not available to new players.

A new player will play with the starting gear, and he will play a random basic T1 mission, not a "special" investigation mission.

If he can't do much and experience frustrating encounters on easiest difficulty, he will ask for a refund.

The game should give a player all he needs to start playing (hence starting difficulty adapted to starting equipment).

A player should not have to go on a forum to know what stuff to replace (depending on the little money he have and the luck of what the shop will offer) and what is the easiest mission to start with.

Bad choice, either in stuff or in mission selection, should not occur on the starting difficulty.

Starting difficulty is for discovering, trying and learning, and have to allow some mistakes.

Punishing (or optimizing from the player pov) is for higher difficulties.

You wan't challenge? Fine, there are (will be) T2, 3, 4... missions for that.

Don't impose it starting from T1 difficulty.

right now for me 'retreat and fire' tactics works much better than covering

under heavy fire any cover destroyed too fast, under light fire i can stand and fight uncovered, HP restored itself before i reach another pack of Emperor damned targets

I can tell you now people are not using cover. I have read so many people complaining about havocs and knockdown. (you can't be knocked down in cover, or so it seems)

From my perspective, the issue of what are the right weapons/load outs is not so much a matter of difficulty & balance but, one of individual play style.  I think that those who are having problems with the game at point are trying to use "favorite" weapons & equipment that don't match their play style. I have experimented with many different weapons for both of my characters to find what works for ME. I may really want to equip my crusader with that grenade launcher because it is "cool", but it is simply not the right choice for my play style.

To me it's just a matter of balance. Certain enemies like the plaguebearer (I think)  are regenerating a lot. I figure this is something that will either be toned down a little, or like you suggest possibly mitigated by player skills/abilities. Remember portals did the same thing for a while? I'm pretty sure this will get tweaked similarly.

Hmm, I swore the plasma gun had at least one AP ability?  I stopped using it when the grav gun came around. :p

instead of feeding the troll we might lobtomize it

Exactly, they're the "intro" missions basically. He wasn't gunning to do a tier 3 hardest cards tarot mission solo. Just a video for newer players who struggle clearing any mission,

That's just the point. Investigations are easy, all the time. The enemy density is significantly lower and there are very few elites. Now compare that to a mission on the rooftop tile in the same tier, which is not part of an investigation. Difficulty spike.

The mission was more of just something in the background. And there is a difference between difficulty and balance. Poor difficulty is where there are random spikes and valleys of difficulty completely randomly and unexpectedly. Poor balance is where the spread is too wide for whatever we're talking about (i.e. weapons in this case, like needle/exitus rifle vs plasma gun/longlas)

Also, people expect it to play like a typical ARPG, which it does not, especially with the assassin. 

Talks about difficulty, plays an investigation mission to showcase - arguably the easiest missions currently available in the game - and to prove his point "it's not too difficult, it's just not balanced, you are doing it wrong when you can't manage to exploit balance properly like I do". One word: unnecessary... Addendum: ...as usual.

Carry on.