The amount of Crowns&Merits earned depends on the number of guilds in the fray or more exactly, it depends on the number of battles played.
So if there are 100 battles played for example there are twice as many Crowns awarded than if there were only 50 battles.
That and only that is why we are still in tier 4. The SPS rewards are already higher in tier 5 as is - making a change to that won't move a single guild to tier 5. We don't care for increasing the SPS rewards if the guild still earns less Crowns than in tier 4.
What we need to fix is the reduction of Crowns&Merits if there are less than 10 guilds in tier 5 - only that will make tier 5 happen.

Also tagging @davemccoy and @clayboyn for this.
It seems like it's not really clear what this proposal would and would not actually do if it was implemented.