A level ten player facing a level twelve player starts the match at a massive mathematical disadvantage before a single card is even played.

Many players inadvertently stall their base progression by hoarding resources or ignoring the social systems of the game.
Gaining XP Through Upgrades
However, the ratio of gold spent to experience gained changes drastically depending on the level of the upgrade.

Conversely, upgrading a card to the absolute maximum level costs massive amounts of gold for a relatively small XP return.
Upgrade your main deck first, always.It is the most efficient conversion rate.Do not upgrade useless cards to high levels just for XP. The Secondary Source: Clan Donations
The second most consistent way to generate base experience is by actively donating cards to your clanmates.

This is why joining an active clan of fifty people who constantly request cards is absolutely mandatory for free-to-play users.
Card RarityXP RewardSkeletons, GoblinsSmall amount of XP per card, but you can donate hundreds of them dailyFireballs, P. Here is more info in regards to tower rush look at the web site. E.K.K.ALarge burst of XP, but highly limited in how many you can give The Margin of Victory
If your king tower was one level higher, it would possess several hundred more hitpoints, turning that loss into a win.

Furthermore, higher level towers deal more damage per shot, altering crucial interactions against enemy swarms.