This still makes no sense. You can just send directly from your own node without ever using their wallet and having them custody anything. One channel is enough . If you don't have liquidity to receive directly then you wouldn't be able to send sats back to your node from that channel. If you do have liquidity then you never needed to use them in the first place.

And again, not everyone can have a node with on-chain channels so doing this round about thing you're talking about is moot anyway to the point I'm making. 

 Say you open a 10M sats channel and send 5M sats to the wallet, now you have liquidity both to send and reciwve without worrying about getting drained or having routes failed or spammed with HTLC etc. 
I have been doing it for a while and it seems to work fine.