I did own 40' Country Coach build on Gillig chassis and had no complain about 2 axles.
Before I did own 20' Class C on Toyota with 3 axles and that thing suck.
So even tag axle adds stability, well build coach can ride well without one, while giving you more storage space and less maintenance.
Than you have to remember that on heavy coach the tag axle is a must due to allowed weight on rear axle and there is no way around it.
I hear about Prevost owners turned around on turpikes due to over weight on the rear axle regardless tag axle.
Also if you tow, tag axle will be appreciated.
Bottom line, if the overweight of the axle is not an issue - drive what you like and see how it handles.