Apologies. I misread your post (read "tfl" rather than "non-tfl" and thought that you were bundling Hex and tfl service together). That said, my reaction was primarily related to the generality of the statement about the uselessness of the journey planner for Heathrow. Your statement was not about the uselessness of the journey planner for the OP or for individuals who use non-tube rail services but about its uselessness for Heathrow in general. That seems to me a little excessive as vast swathes of users do not use a non-tfl managed rail service to get to/from central London and thence to Heathrow. I agree with you that it would be nice to be able to exclude the Hex specifically but let us not forget that this is a journey planner for the whole of London and not specifically designed for airports as such and it is perhaps not that surprising that it does not allow to select/deselect specific train operating companies among the myriad of non-tfl train services in London (although I can see that a case could be made for treating Hex and Gex separately given the specificity of their pricing structure compared to other train services in greater London).

Put differently, the Hex exclusion tick box would be a "nice to have" feature but not having it does not render the journey planner useless for Heathrow services, at any rate not for everybody.