With Wither's new ram attack in MCPE, it can tear giant holes into walls and leave all the block contents behind. When done enough, all the residual blocks could create massive lag, so I'm wondering if there's an area where I can fight the Wither so I can avoid this conflict as much as possible.
I usually go into the nether, and find a place where I can climb up to the bedrock top limit. From there I hollow out a small spot, spawn the Wither, and try and kill it before it tunnels down to far. There's usually less construction in the nether for the Wither to mess up. However, it's also risky to die there and have supreme difficulty returning to collect what items you can.
I ran into the same problem. Couldn't turn, could barely move, couldn't attack, then threw my sword away trying to switch, and died. Thankfully I backed up my game.
I tired at the top of the neither, he just destroys an impressively large area going down. Worst lag I've ever seen. I tried in the overworld at bedrock. He destroyed an impressive area going up. Same result, just darker. So I thought about where could I go with less to destroy? So I just found an area with a few small scattered islands. I figured even if he destroys water, it doesn't break and fall so it can't cause lag. Off course, most strategies are about limiting his movement and this one didn't have that at all. So he was all over the place. It was hard, but there wasn't any significant lag. And I beat him. Only other place I could think of was in a large cavern at bedrock, but I didn't want to take the time to hollow it out.
My guess is the ram attack was designed to make the old strategies not work and force people to fight him in the open. Tempting to get some frost walker boots and fight him over the open ocean, mobility was an issue with my strategy. He would sometimes go half way in the water (ram attack does destroy water, kinda fun to watch it fill back in) but he never went under. He'll attack squid, so you wouldn't be safe under water. But I bet you could put some redstone under the water, like the cobble generator strategy, but coming up out of the water. It would also be interesting to try near an ocean monument since he would be distracted by the guardians.