A ‘T Tail’ increases the elevator effectiveness by giving a larger effective span. High elevator effectiveness is required for high lift wings, which are often mounted above the fuselage, thus the tail has to be out of the down wash. The end plate effect also gives more rudder effectiveness for a shorter tail arm. i.e. YC-14/15, C17, Dash 6/8, and 146/RJ.
The 146 still has the highest Clmax for any civil airliner. Deep stalls? For the 146 in theory yes, but the test team tried very hard to find it yet never experienced any during development. The stick push gives protection, but during certification it was also a quick method of determining the expected stall speeds so that performance testing could progress quickly.