The engineer triangle

Went to a pub server this afternoon playing 2fort as an engineer. Set up the usual buildings then I decided to check out the enemy's base...if lucky I might be able to get into their intel room. Went into their court yard, but killed by a level 3 sentry. Then when the camera zoom into the one who killed me, I see something which I called the "Engineer triangle".

up the stairs of the court yard I see a level 3 sentry and a dispenser standing beside each other. then on top of them is an engineer, constantly hitting the sentry with the wrench while being healed/metal resupplied by the dispenser. Now here are my questions:

-Would this defensive method last long in pubs?

-If I were to get rid of that "triangle" which class besides the spy would be a good choice? and what are your way(s) of donig so? (if you are alone facing the triangle)

If its just one engineer, humping his gun, killing it could never be easier as a demo man.  Stand underneath the courtyard catwalk, or anywhere else that you cant be shot at by the sg, and lob 4 stickies all around him and his set up, detonate them all at once, then shoot some more regular nades to clean up the rest, and kill the engie.

That sentry is actually facing in a direction where it can detect anyone (except enemy cloaked/disguised spy) coming from both paths...its hard to stay under the catwalk without being detected.

Just shoot the wall next to it with 5-6 stickies and that should be enough splash to get it, maybe even less if it is closer than where I am thinking. If you can't get stickies near the sentry, just use a few more stickies a little farther away. You might not kill everything but at least with the sentry gone you can go in and get better aim. But I don't really see how it could be anywhere where you can't edge around a corner, a picture would be helpful. Either that or say which stairs it is, there are 2 sets of stairs in the courtyard, 3 if you count the one going to the intel.

----------------------------------straight stair entrance to intel
|   D,lvl 3S
|
|
|
|
Battlements

Somewhere around there if you understand my diagram

----------------------------------straight stair entrance to intel
|   D,lvl 3S
|
|
|
| x
Battlements

stand where the x is and shoot charged sticky shots at it(you might not need to charge at all, not sure). You should be shielded by the catwalk. If you can't see it, like I said above, shoot the wall next to it. 3 or 4 stickies should get it done.

If the catwalk doesn't shield you stand even farther back (where you would be under the spawn area) and shoot charged stickies, crouch if you need to for a clear shot.

Of course this only works if it is undefended or the engy isn't paying attention, but it shouldn't be easy to take out a defended sentry.

----------------------------------straight stair entrance to intel
|   D,lvl 3S
|
|
|
|
Battlements
         x | Spawn
     x     |  room
------------

yeah...since it was constantly being repaired, I probably would need someone to help me distract the engineer on top of the buildings before I can get them.

If the sentry is on that side, you can rocket jump into their battlements and lob rockets at it. The range isn't long enough to reach their battlements, so you can chillax and fojax.

true...would need to take our the snipers first though. When I was in that server, there were at lest 3 snipers each on both decks

Demoman or soldier will easily do the trick, unless its some intensely placed sentry gun location that I dont know about. But judging from your diagram it isnt.