Quality T-rails tables can be set up to play as well as any & the rails can be as solid.
Witness snooker tables, e.g.
The difference is that T-rails can be more difficult to set up well.
Consider how the rail bolts into the edge of the slate - there is no leeway to adjust 2 adjacent rails along the side to be perfectly aligned, if the wood in the rails has compressed differently, the rubber is slightly different, or the original machining of slate & rail was a little varied. To change anything requires either careful selective (hand) planing the rail mating surface, or shims. Of course if shims are involved, some of the rigidity can change. etc.
OTOH if everything is perfect or close enough to it, the T-rail system locks that in without any further adjustment.
Nonetheless, for modern systems bolting through the face of the slate allows a bit of adjustment for alignment. If the rail bolts remain torqued (not always a given, either) the rails will stay in alignment and remain sufficiently rigid.
Based on geometry, for 1" T-rail slate, a ball strike to the rail has less leverage to react the bending force since the fulcrum (the bolt) is lower and there is less behind (below) it for reaction. A "modern" face bolted rail has some advantage, again, if the bolts remain in torque. But the modern rail is still bolted through a slightly giving element, the cloth. (as is T-rail, though less so, at the edge) I wonder if the old 1-1/2" T-rail slates might have an overall advantage, ignoring the niceties/details of setting up?
Practically, given time & insight, it seems that most quality tables that are not deteriorated can be set up to play as well as most any other.
Garczar - thanks for that great link!
smt