I know that multipools like Prohashing or Nicehash already exist, but the problem is they don't support all algos and they charge high fees.
I'm thinking of developing a website that takes in withdrawals from various mining pools (ETH, ETC, CFX, RVN, ERG, FLUX, SERO, FIRO, etc.) and auto-trades them to one output coin, like ETC or LTC. The website then instantly deposits the single coin to your output wallet for a small fee (~0.3%).
Under the hood, all the wallets will be hosted on an exchange like Hotbit and trades will be performed on that exchange. Security shouldn't be a problem because all incoming deposits are traded and sent out in seconds.
With this service, you can always mine the most profitable coin (which will more than compensate for the 0.3% fee) and receive the earnings in the coin of your choice. You can also track the revenue history/prices of each algorithm over time. You can use any combinations of pools that you want, like choosing those with the smallest fee or the best reliability. When the market becomes unstable after ETH PoS, mining the best coin out of several choices will only become more important.
I want to know what the community thinks of this idea. Is it unnecessary or is it convenient?
You mean pools like zergpool.com or zpool.com or mining-dutch.nl? This are very old pools with the ability to mine much different coins and you can choose in what you get paid.
2miners also give you the ability to mine ETH or ETC and get paid in BTC or Nano
You have a big problem in you idea - different algos need different miner setups - so you need something to switch the miner or so. So it is not so easy as you think