It's a supposition as Crossrail hasn't opened yet, funnily enough!
I am well aware that Crossrail has not yet opened but as the statement was made in the present tense I assumed it was based on some passenger flow studies. From your answer I see that it refers to a future possibility rather than a present fact.
However, I can't imagine many business travellers from the City or Canary Wharf taking a taxi to Paddington to catch HEx after Crossrail opens, it would be bizarre. You'd either take the taxi/private vehicle all the way or Crossrail.
Not all passengers for Heathrow, either now or in the future, will come from the City or Canary Wharf. There are large areas of London which will not be affected by Crossrail and for some of these Paddington will remain a useful node. Paddington is convenient for large areas of Kensington and Chelsea, Notting Hill, St. Johns Wood, Camden, Marylebone and Westminster which are not served by Crossrail at all. For all these and similar areas such as those on the Bakerloo Line corridor south of about Willesden to Lambeth a fast service to Heathrow with a change at Paddington will remain attractive. Over the last decade there has also been significant office development within walking distance of Paddington station which also generates traffic.
From personal experience, HEx gets plenty of leisure customers anyway,
Interesting, as Minstral25 in the adjacent post stated:
Heathrow Express is like Gatwick Express a vanity service only for wealthy business persons.
You can't both be correct.
as the Connect service is less frequent and not as "publicised". Once Crossrail opens, that will change
True. But as Connect is the local train service on the Great Western its transmogrification into Crossrail will mean that the inhabitants in that corridor will have a faster route to central London than they do now. Crossrail itself speaks of bringing another 1.5 million people to within 45 minutes of central London. This is expected to be the big change and is the main purpose of Crossrail - not ease of access to Heathrow.