Sure, when you start out you get out results FAST, but then you run into limitations, weird behaviours and quirks that have to be worked around, and soon everything becomes a mess.
Mind you, I'm a hobbyist in this field so maybe you could chalk it out to inexperience, but I shiver to think to what professional developers have to deal with if the small prototypes I cranked out got so convoluted.
I'm trying out UE4 lately and although it can be daunting at times (and with horrible documentation), it feels much more comfortable to use in the long term.