I will say the Javelin is worth bashing, since there is hardly a kit to compare to it...maybe the CA Widebody.

Yes, the narrow fuse is a problem with the Javelin. As to gross adjustments in servo location, I hardly ever use the stock servo mounts. After I strip the covering off, my next step with an ARF is to cut the servo mounts out of the fuselage. Apart from having DEPS elevator and pull/pull rudder servos at different heights, I like to do a trial CG balance before I settle on exactly where on the fore/aft axis I will mount my servos.

When I do another Javelin (I have two NIB), I'd probably use a low-profile servo side-mounted for the elevator, and live with the plane of output rotation being not quite centered horizontally. If I didn't want to do that, I'd set up a vertical tiller bar to drive the pushrod, and drive the tiller bar with a standard mounted servo. All this sounds like worse than building a kit, and in some ways it is, since it's always easier to build it how you want it from the start.

But the Javelin does fly beautifully, and I consider time spent on these mods to be well rewarded once the plane is in the air.

One of these days Hitec (the great innovator in servos) will bring back the linear output. (Maybe. I hope).

As to the second/third order level of the problem: I think we've seen such great progress over the last couple decades in model aerodynamics that control systems/linkages are to me now first order problems (along with power systems).

But keep all this in perspective: do what you can with your Javelin, and you will most likely have a lot of fun flying it; then get yourself a good kit (Widebody or ?) and pull it all together on that. Working out problems in every new plane makes us better prepared for the next one after that.