Yes, but 343, 346, 744 are all on their way out, phase out having been delayed by availabilit of the A350-900, 787-900 and 777-900.
Frankly, I never understood why they gobbled up 343 after the bust in 2008/09 and kept adding 346, when there were better alternatives (newer versions of A330-300 and B777). They may have been cheap and available, but commonality would not have ruled out getting more A330 in the mix. Their business model used to be to have a young fleet throughout,.
You might want to think about what the A340 and 747 have in common...
Different operators use different business models. There are some operators who don't do 'D' checks - they get rid of them before that. Others are perfectly happy to do heavy maintenance checks on a regular basis. Put a new/updated interior in a 20 year old aircraft and most SLF won't know the difference between that and a new aircraft.
Heavy maintenance on the 767 (and 757) has proved to be relatively easy and inexpensive, as a result there are some seriously high time passenger 767s still flying for mainline operators.