Rethinking my setup. Advice would be great

I have a 5 box team with 1 paladin and 4 shamen. I did this team for a combination of PVE in instances and for PVP in BGs and Areana (in arena I would need a healer to replace the paladin).

I have noticed lately on some videos that 5x shamen teams are able to also do heroic instances and even the new instance with patch 2.4. I thought a tank was required in any lv 70 instance or heroic instance, but it seems I was wrong if you have 5 shamen.

So I am considering going with a 5th shamen and forgetting the paladin. What are your thoughts on this? can a 5x shamen team do everything that a 1x paladin and 4x shamen team do?

They have tanky pets, but they're on a 20 minute cooldown. Every one I've seen that does them with all shammies uses them in some combination to tank the bosses for 'em.

Some encounters that you can do with 5 shamans, you'll have problems with as a 4 shammy+1pally setup simply because you've sacrificed too much dps. Good examples of that could be Heroic Mechanar boss Sepethrea and Heroic Magisters Terrace boss Vexallus. When you get enough spelldamage you can nuke these 2 down before you're even threatened. I'd say 600 spelldamage is the limit to be able to do encounters like this with 5 shammies, and even then you'll still need some luck. With 800+ spelldamage on 5 shamans it becomes easy I'd say. 4 shammies with 600 spelldamage + a paladin who really doesn't bring any dps, both encounters would be very difficult. It would of course be possible (everything is possible), but with a paldin + 4 shammies you'll need to micro alot more to be effective.