I've lived next to LCY for a long time (actually for longer than the airport has been there).
Two of the limiting factors must be the bridges over the docks at either end of the runway, higher than the runway elevation. The irony is both these bridges are new, and have been built since the airport was established. That at the eastern end is only about 5 years old; it was rebuilt with the road deck higher than the old one
. Its predecessor was a lifting bridge and the glidescope must have allowed for it being raised (which nowadays is required about once a year !). The swing bridge at the western end doesn't have this lifting problem but was built for some reason with a large elevated control room which again must determine the glidescope on 10 approach.
There's also a large tall warehouse (the white one) at the western end which may affect things. It has been abandoned for at least 20 years.
Only very occasionally do large ships still come into the docks (for example Warships come up to the Excel exhibition centre for the military trade show), and I believe as they sail in past the runway they affect the ILS glidescope.
Overall a lack of joined-up planning I'm afraid. Both bridges could have been designed differently.
I'm just wondering, mentioning LCY 146 MTOW restrictions, how others manage, such as Swiss to Zurich (half as far again as DUB), who use -300s, and in the past Malmo Aviation worked to Malmo, well over double the distance of DUB.