We've finally learned to risk doing more things on our own, even in non-English speaking ports.
That sounds like a lesson learned but it can also be a false sense of security. There is often savings in time and cost through outside sources. There is also higher risk involved. If you book cruiseline excursions, they know where you are and if your party is late arriving back, they can get in touch with the tour provider for details on the delay and hold the ship until resolved. Out on your own you don't have this layer of protection. Also the lines screen their providers and if one gets an abnormal number of complaints or serious complaints that are not resolved, they will drop that provider. There are some great outside sources and not so great. You have to do more homework to be sure you're going to get what you pay for and will enjoy it. There is also things like, are they fully insured? If something terrible happens, where will you go for resolution?
Don't get me wrong, I've done outside excursions and ventured on my own with no excursion. When I do, I have travel insurance of my own purchased before my trip. I'm careful and check with sources I know and trust for advice before using outside sources in most cases. I'm not advising you not to go it alone or use independent vendors, just understand there is a difference in making that decision in a number of ways.