Tabardariyya suffers from the same bug as the Mutatawwi'a, so avoid them for now.

Halberd Militia do not suck; they have that h4x animation like the JHI and the Zweihanders which simply allow them to massacre most units. Just keep them behind your spearwall and counter-charge breaches and cavalry.

The purpose of Ghazis is that they are cheaper than dirt and have good morale, so they are great for scaling those ladders of doom. You won't even feel anything even if 10 units of Ghazis just died out clearing those battlements. This is what they are great for.

Also, I'm quite sure that the racing track gives Arab cavalry, not Desert Cavalry.