Not sure about the engineer, but they have stated before, they made the gun really accurate so it at least posed some threat to high level players, but it does kick up a storm of death for ones who don't know how to uber or spy.
Of course, rebalancing one class changes the balance of all the others.
Of course, with the new lvl3-dispensers a destroyed sentry can be rebuild in no time, so a half-successful attack which might have given you a foot in the door previously has far less impact now.
It did change my play slightly, whereas before I would focus on taking all the sentries at the cost of everything else, assuming that someone else would easily follow up and take out any other buildings, I now have to hit dispensers as well. Means, if I want them to stay down, two SGs with uber is pretty much the limit, unless the building placements are in my favour.