I agree changing the fixed value from 20 to 10 will still leave the system highly favoring large guilds. However, the reason I am suggesting this is because the developers were looking for tweaks that were easy and consistent with their goals. Merely changing the fixed multiplier accomplishes the goals stated earlier in this thread while giving all guilds a chance to advance beyond where they currently are. It won't allow many small guilds currently stuck to advance to 100, 90 or even 80 but the biggest benefit is that it would allow guilds stuck below 55 to get the bigger ship. This should also be good for Turbine as that almost all guilds able to buy the level 55 ship with astral shards will do so rather than live with the level 50 plat ship.
While your guild was stuck at 80 prior to the change there are plenty of small guilds stuck at a much lower level. If they are willing to let large guilds like yours get to 100 without a decay impediment, I am not sure why you or the developers would wish to prevent these lower level small guilds from getting their level 55 ship. It's obvious that your only goal is to ensure that large guilds have an overwhelming advantage over small guilds. I am not sure why the developers would be reluctant to make such a change unless there was a hidden goal of keeping small guilds dependent on guild elixirs and store shrines. Since they are silent on the issue I will assume they are being honest and this is not a goal of the system.