No one should go solely on anyone's word. Learn how the piece of equipment works and then consider the advice.

Dropping down a housing size is like dropping down a garden hose size etc. Physically speaking, there's going to be more water pressure through the smaller sized hose... however if the flow rate increases (tap is turned on more), then you'd do better to upgrade to a larger hose to benefit from the larger volume of water etc. It's exactly the same with small/ large turbos. The larger the exhaust housing, the longer it will take to reach efficiency, but when it does it will flow more than a smaller housing that will usually become restrictive at similar rpm. However, due to exhaust gasses running through a smaller area/ housing, will spool up the blades a lot faster and so on.

The basic idea above could never be found to be "a crock of shit", because it is measurable and can be tested over and over with the same results. Something I wish could apply to differing mechanical advice throughout the metro area!