I wouldn't say "punching bag" is exactly the right phrase, but it would be a difficult position for both of you.
Even if your partner has the best of intentions, he can't help being influenced by continually hearing and reading Watchtower teachings about being "unevenly yoked" to "worldly people". He will hear that his duty is to win you over to "Jehovah's Organization." When privileges are assigned within the congregation, he may be passed by in favor of another "brother" who is married to a "sister", so if he ever aspires to be an MS or elder having a wife outside of the congregation can lead to resentment.
Couples have challenges. Cars break down, jobs are lost, children act up... I would hate to think he'd have nowhere to turn. I already hate that we wouldn't be able to go to the same spiritual source for support.
You bring up an important point. It is easier make a mixed marriage work in the times of "for better... in health... for richer", but when life leads to "for worse... in sickness... for poorer" people revert to their inner self. Your moral compass guides your response to difficulty and crisis, so dealing with difficult times is harder for marital partners with conflicting spiritual backgrounds.
Consider this worst-case scenario (may it never happen to you!) Suppose one of the children was in an accident, and the hospital determines that a blood transfusion is needed. You say "yes", the Watchtower says "no," and your spouse faces a dilemna. If you marry a Witness, this is a real possibility, not just a hypothetical situation. Are you (plural) prepared to face it?