A few coincidences do not maketh a conspiracy which is another way of saying correlation is not causation. You said as much yourself: "No one knows why it happens. Whether it's a genuine technical fault or a conspiracy. But it was what it was." Question: when is something ever not what it was?
I'm rather given to think your title was actually click bait, at the very least it should have had a big "?" at the end of it.
Maybe instead of a conspiracy, they are just a rapidly growing company having to deal with tens of thousands of new customers per day and massive ICOs generating huge volumes of transactions which are often backlogged on the respective blockchains anyway? It's not like they aren't making money out of every single transaction that passes through them - what is their incentive to throttle that and try and impact the market in unpredictable ways?
Sorry I'm just not seeing it.
Your final advice: "have caution while dealing with CoinBase and decide it's efficacy by yourself." should be applied to all companies. Remember the beauty of the current blockchain ecosystem is no one forces you to hold you funds with CoinBase or any exchange. You can just hold them all locally in a wallet and contribute to ICOs at will, and make trades on distributed exchanges and places like BitShares.
Ultimately anyone who didn't get to sell last time BitCoin crashed is probably happy they are in at BTC/USD $4000+ now. You'll also notice that when the ETH flash-crash happened CoinBase made good on the issue caused by their GDAX exchange an its lack of liquidity - which ultimately wasn't their problem at all. The blew several million dollars making customer happen anyway. And the lucky trader who bought ETH for pennies of the dollar during the crash - kept his money just the same.