Large guilds have been whining for a long time that their players are leaving for smaller guilds because they are not advancing, these changes will completely reverse that situation. If what the large guilds have been saying is true then it should follow that people in small guilds that have stopped advancing will jump to large guilds.
Personally I don't know anyone nor have I even heard of anyone on my server who'd have left a large guild specifically because they were not gaining levels. On the other hand, I know some people who joined a large guild only because they already had all the significant buffs. Many of them later left those guilds when the smaller guilds had started getting those same buffs too.