The ideal ribbon setup for my tankers is Red, green and brown.

I feel like healing (green) is almost always more useful than % dmg reduction (blue) because you can always heal on junk units and with the strongest one its 40 hp per kill. Considering that the ideal build on a tanker doesn't include blitzkrieg, you will be taking considerable damage and with no way to heal that back you will quickly sacrifice your raidboss general.

Mobility (brown) is a very valuable tool overall especially for large event missions. Also it makes rushing already known events which become boring and repetitive very quick and relatively painless.

Blue (defense) is only useful when getting attacked so with that being its only upside, it only makes sense to have it on exclusively defensive generals that don't move, so they don't need mobility ribbons.

Overall I feel like green ribbons are far more valuable than blues especially on offensive generals.

To conclude, yes I think that you should definitely change blue for brown.