It is still possible, but yea eveyone is right. For arbitrage between exchanges it can be difficult.
Why not do some tests with a small ammount of altcoin and try to do crypto-crypto arbitrage, learning by doing is the best.
Do not forget to add the exchange fees and withdraw fees charged by the exchanges.
Alt coins are better for starters, because for the most part, you don't have to wait very long for transfers.