IP67 is not bad, but, remember that the immersion limits are TIMED, so its not like a rating for a submarine...and IP68 is typically at LEAST twice as water resistant as IP67 (The 6 is the dust resistance rating).
And IP68 means the entire unit can be ~ 2 METERS or more deep, while the IP67 rating means the top of the unit could be a bit less than ~ 6 INCHES deep to pass.
Those are generally 30 minute or so tests.....so that UP TO ~ 6" for a bit vs up to 2 meters for a bit.
Also - Keep in mind that these ratings are on NEW units. That means water resistance tends to drop with wear and tear, vibration, oxidation of seals, thermal expansion/contraction cycles, etc. A unit that is built to the higher standard, over time, should typically remain MORE water and dust resistant than one built to lower standards.
That all means its a LOT harder to pass IP68 than IP67.
The unit, whatever it is, must be a lot better made to make the jump to IP68 from IP67.
An example of this are the lights for boat trailers.....the lights might get a little dunk when you back down the ramp to get the boat into the water.....and IP67's are considered as not water tight enough, and IP68 are.
If you think about it in terms of a product...if you have, say a gasket that is between two parts that thread together, and an electrical plug that passes through a penetration with a rubber grommet...what's involved with one being able to pass, and one not?
They can look the same...but one leaks more.
SOMETHING was improved, but what?
How about a thicker O-ring, which then required more threaded section to have sufficient seal area? - Which added costs in the metal and machining, and, the quality and sizes of the rubber parts...and so forth...there's stuff involved that you can't see, but make one unit costs more to make, and the IP rating gives a clue as to if its JUST added cost, or, if you get something for it/its a better VALUE.
This is one reason why a more expensive light can be JUST more expensive, but no better in quality...and another can be less expensive, but better made....and one way to tell the difference.
Obviously, the LIGHT emitted is another variable.....but the specs needed to evaluate that part are almost never listed.
Lumens are listed the most often, as that's the easiest to get large impressive numbers for...whereas the cd rating and the beam angle are the most useful specs, and they are rarely available. This is because, again, its easy to make a light that puts out massive lumens, and hard, (for an LED bar), to be made with the amount of throw even a well made 55 watt halogen light can deliver (Albeit the 55 watt halogen will have a small spot, and the LED light bar will have a giant flood, etc)