Can I ask is it bad to have a miner as powerful as realasicminer in the pool ?
It's good, actually.
The higher the pool's hashrate, the lower the miners' daily variance. The expected rewards remain the same, but the actual rewards fluctuate less.
Now, a single fast miner will mine at a high worker difficulty, which means boosting the pool's hashrate without putting a strain on the pool's network and CPU usage.