Sipahi and even janissaries are far too strong. If left alone ottomans are unstoppable. But they are extremely hard to punish in feudal and castle because they have the arguable the best unique units while they getting increasingly more and more free units
Sipahi is too much overrated if they were so op games whould be ended in age 2.Problem is janissary and free siege they get.I actually balanced janisarry in a mod.When janissary first came out it had slower fire rate so they were not dealing any damage.In that mod i didnt changed the fire rate,i increased it range to 5 and lowered bonus damage to cav to %50 of base damage maybe %75 of the base damage i dont remember now.It was perfect but they gone to direction of making them fire faster.
Problem here is those units are actually very weak they only get stronger when you combine them.They counter everything(Sipahi+janissary+siege combo).
Nerfing sipahi was a mistake they die to horseman even before the nerf:
Beasty and some other who see daydream or halucinations while playing this game they say it kill knights and keshik.Show me a proof that they knight and keshik with equal resource and i will accept your argument.Aslong as anti infantry siege exist Ottomans will be op.They are free and come faster then other siege equipment.