As others have mentioned, rangers bring very little value. More scat bikes would give you a better bang for your buck.
Shimmer shields are really bad, mathhammer wise. They lower the dakka-per point of your unit, and also lower the resilience per point. Simply put, with the cost of an exarch + shimmershield, you could buy more avengers and still wind up cheaper.
Massive firepower
The twin linked weapon in the exarch lowers his damage per point. It's a horrible upgrade.
Why the
SL on it? It seems to want to get in assault ASAP, so I wonder if those points would be better spent on another scat bike.