At the moment I couldn’t find any other ISA provider with lesser FX fees, when I purchased GOOGL in iweb isa I was down by almost 2%. I know it pains but there is no other way.
For active traders with large deposits there are better options. For example on Interactive Brokers,
If account deposits are more than $20k then, there are no maintenance fees, you can keep money in USD or do whatever you want. and transaction fee is $1 per trade.
FT could have a cap total fees per year in thousands , and might attract mutli-million account holders? don’t know may be they are with better deals already!