There are several rating systems for climbing. The most common here in the US are the Yosemite Decimal System and the National Climbing Classification System. From the way the original question was asked, I understand "Class 4" to mean a degree of difficulty rated by the YDS.
According to the YDS, Class 4 is beyond scrambling and is actually climbing, often with exposure. A rope is often used. A fall on Class 4 rock could be fatal. Typically, natural protection can be easily found.
A rope is technical gear, and you have to know how to use it. Natural protection is great, but again, you have to know how to use it.
As was aptly stated in an earlier comment, Class 4 is "you fall, you die" type climbing. For me, personally, I get all worked up about the right gear and the right skills when a life depends on it. "A bit of rope and a bit of training" and "playing around on some rocks" is simply not enough. It is how people get killed.
If we were talking about a Class 4 bouldering problem a couple of feet off the ground and with ready access to emergency services I might agree with you. From the way the original question was asked, I understand the situation to have significant exposure in a remote area.
Sorry to be so emphatic, but having seen an untrained and unroped climber fall and die six feet from me on Class 4 rock (while I was putting on my harness and flaking out my rope at the base of the same climb) I can't help it.