I only have the bioload of a betta and tons of surface area in my filter for bb to grow on. And I also use emersed plants then submerse them (the tube plants that you find at big chain pet stores). I don’t like purchasing plants that are already in tanks for the fear of bringing in a hitchhiker (although I have creepy crawlers in my tank now but that’s a different thread). As far as the temp goes... mine has stayed constant for years. I have a thermometer placed on the other side of the tank no where near the heater and it’s always stayed at 78 degrees.I guess it's all relative. I have more bioload in my large tanks. If I can fill my large tanks with enough plants to match bioload, then it's the same. Just harder to fill up a larger tank. There are ways to work around that too though, like using emersed plants. I guess a large tank will maintain a more constant temp, but ime, I change just as much water sometimes as my smaller tanks depending on params.
Every tank is different though. It really depends on what equipment you use and what your cleaning routine is.