The whole LH earning more than SH at the bottom of the payscales comparing with mates not much in it with just the basics.
If you start factoring in spending down route etc unless you are sitting in your hotel room of course. 10 years in yes the gap widens a fair amount. Loads of variables in all the calculations. Living close to LHR means about £5 (£10ish before tax) a day in fuel round trip for me. I don’t mind the crew food and have gone days with only having 1 meal a day at home. Have also done 3 day trips away with lounge access, chilling by the pool, beers, food all included and come back having not spent a single penny. I have flown with skippers who bring their own food or go and grab an itsu before the flight. £5-£10 (as before is £10-£20 from your pre tax) a day soon adds up.
Commuters will have higher costs be it fuel, flying, hotels etc as well.
Year 2 SH and I average £2k per month on mostly day trips. NCP wise can usually get 10 hours quite easily just by swapping for higher credit stuff. Yes I have gone nuts on a few months and pushed out nearly 50hrs NCP, hard to do on SH. LH can get some high credit trips that easily eclipse that in a month.
I boiled it down to career options and being SH the night curfew at LHR is a bit of a god send. Latest I have been walking through my door is 1am. Rare occasion. Even on a run of lates I’m in bed by 11pm 90% of the time.