What are the disadvantages of a Tail providing lift? (tandem-wings included) Most aircraft feature the tailplane configuration, which requires the main wing to provide higher lift than the weight of the plane itself, what seems counterproductive.

Few aircraft have featured tandem-wings like the Rutan Quickie, Proteus or the Maurice Delanne 10 with limited success. I usually read that the main disadvantage of the tandem-wing is that the rear wing is subjected to the downwash from the front wing, what greatly reduces its efficiency Q&amp;A link.

My point it that standard tails suffer from the same downwash effect, and on the other hand this effect can be reduced by:


a T-tail
Making the front wing much larger than the aft-wing.





Thus, which are the flaws of this design (top)?
Given that it could still have the CoG in front of the Neutral Point.
Why are lifting tailwings refered as unstable? Q&amp;A link
Is this layout suitable for VTOL aircrafts, in which horizontal take-off and landings are not an issue?




Thank you for your attention. I would appreciate remarks of any wrong assumptions.

Extra


Why the Proteus features a tandem-wing, and why this layout unusual?


Edit:
The reason for considering a lifting tail is that to make VTOL possible for this layout, the CG must be moved between the rotors, thus far aft.
A lifting tail just means lower static stability.

You are correct, flying in the downwash of the wing makes the tail less efficient. But that does not mean it is all bad: Since downwash increases with lift coefficient, the tail effectively sees a smaller angle of attack variation than the wing, so it maintains a healthy margin from stalling even while the wing is stalled. This helps to keep the aircraft controllable well into a stall (within limits, of course). 

The reduction in downwash as the center wing stalls will even add a positive AoA gradient during the incipient stall which adds some more stability, making it harder for the pilot to command a further AoA increase.

And performance-wise, the download on the tail in conjunction with downwash actually might create a bit of thrust on the tail.

Concerning Rutan Designs: Their different looks are not for better performance but merely the expression of an oversized ego and his way of self-promotion.



EDIT:

The many downvotes I now collect for speaking my mind freely shows how well the self-promotion of Burt Rutan works. But it cannot bend the laws of physics which guide my opinion. Which I will continue to express freely.