I disagree that the MKS and MKT (stupid alphanumerics lead to unending confusion) are too big. I think they are just styled wrong. The MKS is there for people who want a tinier Lincoln (and remember there is supposed to be a micro-Lincoln on the way too, instead of looking like an electric shaver in the front, it will closely resemble a nose hair trimmer).
One of Lincoln's troubles is, they have no consistent design heritage to cling to like BMW, Benz and Cadillac. They went for baroque in the 70's, and those cues just will not translate as well as Cadillac's fins and eggcrate grille, BMW's kidneys and kink, or Benz's ribbed tails and massive shield grille shape.
Like hyperV6 says way too often, "let's face it", Lincoln's design pinnacle was the 1961 Continental. Some of the cues from that car showed themselves in the first-gen MKX front, and the MKT's straight beltline with uptick. But so much of the rest of the MKT is wrong. That sloped rear end and high, narrow taillight band do not help. The band is a worthy Lincoln cue, but it should have had some more definition, maybe some sort of drop along the bottom line toward the outer ends or something.
Of course, the MKX and MKZ too closely resemble their Ford counterparts in profile and general shape. People are not blind, generally.
So the more unique Lincolns are blah and the clones belie a laziness that just will not cut it for a luxury brand.
Plus the powertrains are mostly identical to a Ford, something that has hobbled Lincoln, imo, for many decades.
What to do to fix Lincoln? I would have the designers study the '61 Continental, bring some of that beautiful, pure cleanliness, broad horizontals and chrome-capped, razor-sharp beltline into the future without copying it to the point that it becomes a New Beetle. And I'd stick them on a RWD/AWD platform out of Australia (if it can be brought up to true luxury status with NVH and ride quality). Then I'd design an engine family that starts with a basic Ford architecture, but adds displacement, horsepower, quietness and smoothness.