It's an interesting idea and would definitely change the gameplay a lot - but for the better? I get your point and it actually does sound a bit absurd now that I read your case, but the flaw I see is that you're looking at isolated cards. The change in every card after leveling up opens new opportunities for strategies and tactics. E.g. +1 melee for the Pelacor is the tipping point of it doing 2 damage to a monster with shield. The captain on lvl 9 is a slippery fellow that is hard to hit, and buffs the whole team, while the lvl 4 is merely a sniper.

For me, that is one of the appeals in Splinterlands - it's not only having the higher cards, but also a ton of tactics to consider. So I'd rather stay with quality over quantaty, but thank you for making me think about it :-)