Apparently this is on a workhorse chassis, if the spec sheets I could find are correct. There are some brake system recalls on some of these chassis from that era, so I think it would be wise to verify that they have been done (and get it done if it has not been done yet).
More generally, if the motorhome had not been driven for awhile (weeks or months) before you drove it, it may possibly just be some surface corrosion on the brake discs that had built up, which makes for much less effective braking for a bit until it wears off. This is normal with all vehicles.
If you're expecting hair-trigger sensitivity on a gas motorhome braking system, that's unlikely to happen and probably not really ideal. So long as you can stop quickly in an emergency situation you should be all right. Somewhat heavier brake feel and more sedate response to all control inputs than a car is what I at least would expect.
Don't rely on the leveler jacks or any jacks to safely support the vehicle weight when working underneath it. Proper jack stands (or maybe safe cribbing) should be used for that. For just removing a wheel it may be possible to manage things so that you aren't putting yourself in danger underneath the vehicle, but most chassis maintenance that would involve pulling a wheel requires safe support.
