I don't agree that decay should stay in.
Comparing to the old system, the reduction of decay mainly helps large guilds level fast not small guilds. Large guilds have much larger renown earning potential and a 400 person guild already received over 95% reduction in decay so decay was effectively removed as issue for the mega guilds.
As for small guilds, how fast they get to 100 depends largely on what level they are stuck at which is also based on much renown they earning.
Under the current system a level 55 guild stuck at 55 would gain 2 levels in one year if decay was removed entirely.
A level 60 guild stuck at level 60 would gain 2-3 levels in one year if decay was removed entirely.
A level 70 guild stuck at level 70 would gain 5-6 levels in one year if decay was removed entirely.
A level 80 guild stuck at level 80 would gain 7 levels in one year if decay was removed entirely.
For comparative purposes, a 400 person guild stuck at level 60 under the old system would gain over 30 levels under the new system and the entire reduction of decay would allow them to gain only 1 more level. They are going to get to 100 relatively quickly regardless of whether decay is removed or not. All the removal of decay is allow all guilds to get to 100.
The removal of decay primarily benefits large guilds, but they've already realized most of that benefit from the change in October. The current system balance problems are making it difficult for smaller guilds to recruit and keep their members happy. It punishes guilds for running at a slower pace because renown is based on drops but decay is a fixed daily amount.