I use 100% scoria for my catts (and paphs and phrags and sarco and spathoglottis, vanda, encyclia, oncid, sedirea, dend and angraecum and a phal) in the tropics. I don't ever repot unless the plant runs out of room. And although I don't have as many orchids as a lot of growers ----- I haven't encountered bulb rot for a few decades of growing orchids. I haven't even had an orchid die over this time or run into bulb/root issues - except for a spider-mite related leaf rot on a baby paph, which was eventually cured with copper spray (stopped the rots right in its tracks).
And I only apply fertiliser (relatively weak fertilise) once a month. And also I do the weak mag-cal once a month. First day of the month, I do the weak fertilising. Then 2 weeks into the month ---- the mag-cal. All the rest of the time is just using a garden pump sprayer with nozzle to water the orchids.
I grow the bulk of orchids under a balcony --- so semi outdoors growing. The leaves and stems never get wet, unless strong wind and rain just happens to blow water onto the plants during very strong rainy season. I do have some time on my hands sometimes --------- and I generally apply the bulk of the water around the outside ..... the outskirts of the pot. So I choose a pot that is big enough, and the bulk of the water goes into the media at the outskirts. Much much less ----- or occasionally none - is added toward the centre. So think of airyness and also think of dry-wet gradients, and also think of humidity for the roots, and also think of making things hard for unwanted activity growing inside the pot. Sometimes - people might say a dry out of the media inside the pot is good for the roots ------ but might not also consider that a dry out can make things tough for unwanted organisms in there.
Each grower has their own procedures for doing various things. As long as they come up with a method that keeps the orchids growing nicely (all of them) for very long periods of time (decades, indefinitely) and doing what we can to cut down on chances of disease growing and disease spreading, then that is great ---- and that's the aim. There are always exceptions - where some people grow orchids with their roots in water, and some orchids with root in wet leca plus water reservoir, and may have no problems with their orchids for decades as well. As long as we run through the checklist on what can harm orchids in general (when growing them) ---- such as root drowning, unwanted stuff growing, not enough nutrient or elements into the orchid, not enough water, temperature range and light range and duration, air-movement around leaves and stem and through media, not allowing temperature of the plant or portions of the plant to change very quickly or abruptly etc ..... then we can cut down on problems a lot.
If 1 or more of those things is/are overlooked, then we need to do something to not overlook it.
For sure - there are considerations to be made about media accumulating salts. So if the watering schedule involves continual bombardment of the media with fertiliser, then that needs to be taken into account. So I can understand the need for some people repotting every once in a while. And I also understand that some areas and regions have insects and snail and other attacking animals that need to be considered. But assuming that kind of thing is all under control ------ the important thing is 'the checklist'.
A lot of us here are very experienced or long-time orchid growers. So this is just a friendly sharing and discussion of information. We just pick and filter what we need to make sure our orchids stay healthy in our growing areas.