There is clearly an aspect of marine aquarium care that is more complicated and difficult to explain until you are actually taking care of a marine system. But most of this requires a level of knowledge and dedication to learning, not necessarily physical labor. It all depends on your definition of "time consuming".
For me, doing a 50% weekly water change on a Discus
tank is something that I would find frustrating and would ruin my enjoyment of the aquarium. If my 180 were a freshwater tank, I would despise cleaning the canister filter every 2 weeks and changing 30 gallons of water weekly. I won't commit that level of physical labor to the tank. I'd rather run tests and add chemicals, and empty the protein skimmer collection cup when needed.
When it comes to marine water changes, I don't have a set routine. I do believe there is value to replacing water, and I do change some water every month or so. But this amount is much less than 10% weekly. There is no chance that you will find me replacing 15 gallons of water each week on my 180. The actual level is closer to 5 gallons every other week. It will be nothing for me to go 2 months without a water change at all, provided the alkalinity, calcium, and nitrate levels are not presenting a problem. At the same time, if I felt my system needed it, I might change 5 gallons daily for 7 to 10 consecutive days.
Personally, I largely base the level of care on the size of tank and quality of filtration. On a 29 gallon aquarium with a hang on protein skimmer, I would probably change 5 gallons of water weekly, an amount greater than what I change on my 180 with sump and ASM G3 skimmer. With experience and dedication to learning, you be able to recognize the needs of your individual system.
Most rules of thumb are just in place to help guide a beginner in the right direction, so take these sorts of discussion with a grain of salt. In practice, do the tests needed on your tank, watch how your fish and livestock respond to water changes, and adjust your routine accordingly.