Water changes do not harm the bacteria unless you forget to dechorinate the water, and even then when the colonies are mature that does little harm. It's when the colonies are first growing, like yours, that you have to be sure to use dechlorinator. Though the fish don't like chlorine much either.
The filter bacteria grow tightly bound to the biofilm. The biofilm is tightly bound to all the surfaces in the tank. The bacteria prefer to grow in the biofilm on the filter media as that has the best water flow though it bringing food and oxygen. In most filters, the media is also in the dark which the bacteria prefer, though with the biorb's biomedia being the substrate that doesn't apply in this case. It is not easy to dislodge the biofilm, though hard scrubbing of things like filter sponges can do so, especially with immature media. With the biorb's bacteria being on the substrate, you'd have to really scrape it hard to dislodge the biofilm.
As long as the new water is dechlorinated (to protect the bacteria and the fish) and warmed to the same temp as the tank (so as not to shock the fish) it is safe to do a 95% water change. That's just about as much water as you can get out while still leaving enough to cover the fish.
Whitespot will disappear from the fish but it doesn't mean it has gone from the tank. It is a parasite with a three stage life cycle. We first see it as the white spots on the fish. It is attached to the fish inside a coating, and feeds off the fish's skin. It is on the fish for a few days before each parasite grows big enough to see. The coating protects the parasite and medication can't get at it. Once the parasite has eaten enough, it falls off the fish and lies on the bottom of the tank, still in its coating, and multiplies. The medication still can't get at it in stage 2. Finally, the coating splits open and releases free swimming baby parasites which set off looking for a fish to infect. Stage 3 is the only one where the medication can get at the parasite.
There will be some of each stage in the tank at any one time. It is important to keep adding the medication as the instructions say to make sure there is some medication there when every last one gets to stage 3. If the instructions say to turn the heater up, that's because this lifecycle goes faster in warmer water.
If you need to do a water change on non-dose days, add the amount of med needed to treat the volume of the new water you put back in to replace the amount you've taken out.
I've heard that comment about biorbs before
They can be nice tanks as long as you are prepared to work with their limitations.