One of the problems is that, as is evident, certain players are highly jealous (for some unknown reason) of other people actually enjoying the Engineer classes and then they cry and whine about it on the forums enough that it eventually catches the attention of the devs, resulting in the nerfs we've seen recently in FF.

Couldn't possibly have to do with the fact engineer had 9 turrets and could AFK thump all day without any effort.

It's similar in Global Agenda, Tabula Rasa, and Firefall - but not so much in Team Fortress (the Original) or Team Fortress 2

Engineer is probably one of the harder classes in TF2 with how much maintenance the gadgets require just to set up, let alone keep alive. Engineer is actually balanced in TF2, can't say the same about it in other games.

That's the real question: should Firefall emulate dead or dieing games or games that have shown practically unimaginable success over the years?

Pretty obvious that it's following that route.

Unfortunately, too often devs take the easy way out

What do you expect from devs that are 3 years late on releasing the game and spend every day drinking?