LGW is my second choice of LON airport exactly because of through trains days and night - but for sure I have used LGW once only one way outwards during the entire Thameslink night blocked route, because faffing around with buses in the small hours put just that too much extra time into the journey (up to 90 min each way at certain periods of the night) and it happened that flights more towards the middle of the day were less suitable.
I'm sure it has a big impact.
It really was a pain in the preverbials. I had to catch a flight from LGW at 6.30am; had to leave LTN at around 2am! 1 train an hour (which I almost missed!!) and then having to find a bus stop (which wasn't clearly signposted from the platforms) in the freezing cold to get to London Bridge.
This is also ridiculous - 4.30am on the FCC line is the beginning of "anytime" fares - peak.