It will never really make sense to those who haven't been tuning and building boxer engines for years like us. The way the exhaust pulses are, it just requires/demands more exhaust flow compared to an inline 4. It just doesn't make sense on paper, never will, but years ago we tested .63 30R and 35R turbochargers, and then swapped to .82 housings and picked up 50hp with little penalty in lag (penalty in transient boost response however).
If you compare the turbo/hp from a boxer motor to an inline 4 like a Honda or Mitsubishi you will see the trend we've been dealing with for years building boxer motors to put out 700+ hp.
We could put together a 700+ hp FA20 no problem it will just require $12k in driveline parts
and I'm not ready to pioneer that. Ha ha.
With all that said the smaller turbochargers have their place. We don't drive dyno plots we drive our cars and for some on early and hard provides enjoyment and suits their style. For others like me on a little later but longer with more HP is better.