The reason why those explorers can't compute the same fee as Electrum does is because they're not taking the virtual size in consideration.
And SegWit transaction's "virtual size" is lower than its "size", so the fee per Byte will always be computed lower than fee per virtual Byte when it comes with SegWit.
But when it comes with prioritization, miners will take what you've set in Electrum because it's actually "sat/vByte" although it's displayed as "sat/byte".