I prefer to use Mycelium for fee purposes because electrum does take much higher fee than mycelium.
False. Electrum always allowed you to set up custom fees. Plus, even while using their fee slide, you could select a fee of 90 sat/byte, while Mycelium's "cheapest" fee option was ~140 sat/byte+ IIRC.
If you can't select all the way down to 0 or 1 sat/b (as has gotten nextblock confirms when I looked at recent blocks within the last day), it's not 100% custom.