Does anyone here think that exchanges slow down transaction times on purpose so they could manipulate your funds in the meantime?
Yes, scammy exchanges have been doing it since day 1, Craptsy was a great example when they held Doge when it skyrocketed and then dumped your coins then bought them back when it tanked and gave you those coins a few days to a week later. Trying to arb is impossible on a scammy exchange.