RaboBank have had that message on their website for a wee while. It is surprising honesty in some respects.
I was told before that RaboBank Ireland deposits are reinvested by RaboBank Netherlands in money market investments etc. Hence, the rates of return bare some resemblance, minus margin, to money market rates.
Meanwhile, other banks use deposits for help fund domestic operations.
Hence, it is not really a case that RaboBank 'can't compete', it is just that Rabo make different use of their deposit funds. That different use of deposit funds can only result in lower rates, that is, if they want to do it on a profitable basis.
Rabo could choose legally to make a more profitable, but riskier, use of deposit funds but choose not to.