This Problem is far more pronounced in overgrowth of the 2 maps. Other than the Marquis BS there are 2 glaring locations that the Sentry is easily LOS’d and can do nothing to protect its self.
The first is the side bunker, not only can the sentry be easily cheesed but it is incredibly hard to remove a threat from this location due to its small entrance. I can’t tell you how often me (as Reyna) along with a Montana, ISIC, or Galilea have simply stood in this location and could not be pushed out, simply dealing with threats while putting free damage down on the sentry.
The next rather obvious location is the supply bunker, while (somewhat) easier to access it has the advantage of being completely safe from the sentry. Not only that but with a thumper and supply station at your back its near impossible to push someone out from the sentry side if they are ahead in levels.
I won’t comment on echelon yet as I can hardly seem to get it.
In a supposedly competitive game all cheese tactics should be kept to a bear minimum and ones of this caliber should never have existed. Sure a small safe zone could be acceptable as long as its fair and has counter play but a location that is completely safe from the game mechanics them selves is unexceptable.