Can't say if they are compiled to native code or not. They are at least compiled to Java Byte Code as I understand it. I think you are looking at the problem from the wrong point of view. These IDE's are doing a lot under the hood. For example, each time you change a line of source, in the case of Eclipse I think each time you write a token, it goes and performs an error parsing, there is tagging going on in the background as well. There are so many bells and whistles that it is difficult to even find how to configure them. I liken the experience to needing to be a word power user as oppossed to just a user if you want to get the true performance out of these "modern" IDEs. You can fairly easily turn off most of these features and I think you will find things speed up. Although with a modern PC with sufficient memory I can say I dont really see any performance issues and SW developers will target what they can do based on this.
Most chip companies have adopted Eclipse as the base for their IDE as it provides so much and they just add their plugins. For this they get multiplatform support which is something you dont get with most of the older free IDEs like MPLAB. Microchip chose Netbeans beacuse they thought Eclipse was too complex for Embedded projects. So that should give you an idea of whether Arriba is a good direction for you.
I hated Eclipse when I first used it as part of the Xilinx SDK, it has gotten better and now I rely on it for a lot of things.
There are other non Eclipse/Netbeans IDE's out there. Usually not free and just as much work to integrate. I think you will find given the time MPLABX is actually better at a lot of things than MPLAB8 in terms of editors go. Ultimately it is the direction Microchip has decided to go and most others are very similar so unless you want to handpick your tools you are pretty much stuck with it for better or worse.