Umm an engineer is an anti vehicle class. That's there medium-long range engagement. The carbine/PDWs are to make sure they don't get ganked when someone gets close to them. If you want medium-long infantry engagement thats what assault and support are for. The whole point of classes is that they have strengths and weakness, med-long infantry is engineers' weakness.
Well engies do have DMRs at their disposal. I know most people aren't a fan, but I really enjoy the challenge and can hold my own at most ranges. Even close up with canted irons you can honestly go toe to toe with most players if you can aim. Sure you have a disadvantage in speed, but if your opponents aim isn't dialed in it's not difficult to land 3 shots to the chest. Personally I find the engineer class to be the most flexible class in the game.