What this means is that the higher level quest orientated player will not be able to complete with the slow builders who are the same level as they are. They will not however have the defences to defend these larger attacks, nor will they have the decorations and farm-house upgrades necessary to support as large an army.Be able to send more soldiers in attack but can also be attacked with more soldiers.
This is because the player who completes quests instead of focusing on building and upgrading will: If you are a player who focuses on completing quests, you will not be as strong as a lower level player who focuses on building there castles. The fastest way to level up in the game is to complete quests. There are two aspects to levelling up (besides the mostly insignificant 60 rubies you receive for doing so): new buildings/upgrades and more waves/more soldiers and tools in each wave.