smaller transaction difficult?
The only thing that counts when it comes to Bitcoin fees is the amount of data in the transaction. It has absolutely nothing to do with the value. A $1 billion equivalent transaction with one input would cost less than a $10 transaction with two inputs.
What costs is the storing and processing of data. Every input adds to that cost no matter how small it is.
I don't know how many inputs or outputs that Wirex transaction has, but even a 1 input transaction often attracts a $1 fee. This is a relatively new problem for Bitcoin due to it having a maxed out network and also because the BTC price is so much higher than it used to be and fees are priced in BTC.
A $200 Bitcoin would have 1/10th of the current cost in dollars for a fee. Bitcoin fee pricing has been reduced once before. I don't know if it'll happen again.