Bitcoin was in my opinion never the best cryptocurrency for arbitrage trading. There are other cryptos with faster transactions and low fees. But as soon segwit transfers are the new standard, also little differences could be worth for beeing traded between exchangers.
It was the best because it had the highest volume and largest orderbooks. Sure, you see wild variances in other alts but a few BTC worth of orders would clean the slates at most of the small exchanges and dexs. Arbitrage of course works a lot better when markets are adjusting to the volatility of Bitcoin - sure, these recent weeks have seen it stabilise, but try have a peek during the next bear/bull - those variances will become larger.
It will be more difficult to arb trade now with regulations in place - the volumes of South Korean ones will now be closed off to foreigners, but you can always find people looking for a loophole (check out some of the offers for people looking to partner with locals there and on LCB, for example).