I don't think this is correct. The fastest way from Reading to Heathrow is into Paddington and back out on HEX, which is even more expensive than the 'not via London' fares I quoted above.
I had to exclude HEX to generate the below itinerary using Trainsplit.
And 3 changes with luggage?
View attachment 171995
I said train via Hayes is only quicker to T2/3 and T4 which it is, and so not sure why you chose T5 as a comparison . Also, your journey option is bizarre given the 1512 would have you in T5 for 1616 not 1625 is it claims! For some reason it can't select the actual trains between T2/3 and T5.
1459 arrives 1551 into T2/3 and 1557 into T4 change once at Hayes (so 52 and 58 mins respectively)
1512 arrives 1606 into T2/3 and 1612 into T4 change twice at Maidenhead and Hayes (so 52 and 58 mins respectively)
These two repeat both every 30 mins giving a 15 min service. The Maidenhead change is same platform, but I'll give you Hayes is a bridge/lift. However fighting the crowds through Reading station is far from easy.
RA1 at this time is only every 30 mins at 1457 and 1527 taking 52 or 53 mins to T2 and 61 mins to T3, T4 would require a change at T5 and even using the quicker local bus would take over an hour.
The other way T4 to Reading is 1445 arrive 1542 and every 30 mins with just one change at Hayes. T2/3 is 1455 arrive 1445 and every 30 mins (so 57 and 50 mins respectively). Railair is also every 30 mins at 1437 from T3 and 1440 from T2 arriving Reading at 1544 (so 67 and 64 mins respectively). Add 10-20 mins extra for T4.
So Railair is not quicker. at all, let alone significantly quicker, and is less frequent eastbound, except when trains don't run or to T5 where it wins. However, should it run at all, no. It's just a cash cow for First that justifies them not giving Hayes a better service from Reading and fleeces longer distance passengers. It can be cheaper, but only if both ways are in peak. If one way is off peak it's the same price and if both ways are off peak it's more expensive.
I give you the argument if you live in Reading, or soon near Winnersh, but for longer distance passengers it offers little and it isn't aimed at Reading locals, it's marketed for GWR longer distance passengers. If it's sole real purpose is as a local bus from Reading to Heathrow then it shouldn't charge such premium fares, just as the excellent 730/731 to Basingstoke doesn't.
From the new timetable on Jan 19 Railair becomes every 20 mins but gets even slower to Heathrow but speeds up slightly from Heathrow but is still slower than the train is from T2/3. The idea we are running Railair coaches along a route that has perfectly adequate rail services is ridiculous.
Lastly, advance fares to Heathrow via Hayes are often little more than Reading advances and massively undercut those that use the Railair, but obviously these aren't promoted by GWR who'd rather fleece people to justify to Railair.