-1 for removing the most fun arena. The pillar/lava pool level is great for a few reasons. One, and the most biased, it is the largest and offers great rewards for good long range casters/bow shooters. Two, the lava is NOT difficult to avoid, just do not run near it and even tremor will not knock you into it. Three, the pillars and those steps at the end offer great utility.
The biggest argument for not removing the lava is that the pure size of the level, which in NO way forces you to get near the lava. It may take you a bit longer to get to the enemy, but you will be safe from lava if you stay about 10-20 blocks from it, which isnt hard at all due to the levels size.
You mentioned Quantum Leap. This skill is gimicky (in skirms) and can put you in the lava only if they are already there and you are close. I suggest next time you see a leather clad caster jump into lava you back up out of range and start laughing.