For rifts there is one thing that is way better even than max res: being ranged.
Just respec from dgaze to overkill, and from RM to glad dominance. Mix in some more dex crafts, split stats between more dex and vit to reach max block.
Max block allows you to block some types of elemental projectile attacks, I'm not sure which ones exactly but that is massive bonus. That plus fact even vs physical, 200k def (no runemaster) + maxblock is already significantly better than 700k def with no block imo.
Overkill is also very powerful at clearing small/medium packs, 110% wdm multihit, you can slowly clear much tougher content than as melee.
As for some of the gear. Warmonger helm is very good if you wanna speed up clearing easier content, like duncraig/fauzt, these splash hits 1-2 shot area around your character, and deathgaze projectiles chase stuff thats out of range. It is amazing. I can see if you are not impressed by it, if you want clear tough content, slow-clear high rifts, then its not what you are looking for. But vs normal ubers, it really is much better than other options for melee imo.
Otherwise as mentioned earlier, witchhunter helm with great stats and 2 all res is hard to pass for rifts.
As for switch, I'd argue you may get more value out of colosseum oskill sword, you can use that vs bosses for all the debuff and -100% defense. It is really pretty neat buff.
In general I would'nt stress too much about deep rifts with melee axe barb, its strict anti-melee content, its annoying even in low rifts, where you sometimes get hit by volley of 20 missiles offscreen that can seriously surprise you. As ranged spec that constantly sutter-steps moves around and throws, this is never a problem and you start with huge advantage.