Yep. Even worse when you can pay to get better, like MTG, or Magic The Money Gathering as I'd like to call it.

Once someone in your group starts hunting down those rare (and expensive) cards, everyone else will have to do the same or give up playing.

Thankfully, printer ink (just about) remains cheaper than Magic cards.

You don't need printer ink. You can print them in grayscale, or cut some index cards to fit into sleeves and write the name of the card you want in pencil.

I use a bag of coins I've collected, each coin represents whatever card I need at the time.

Just do it mentally and keep the game in your mind.

"I summon the Whoore Of Babylon, 70/30 flying. You're finished".

No game is perfectly balanced & no players are perfectly balanced either. I don't know about mortal kombat, but home versions of games had handicap features built in for situations like this. You can also do some out of game handicaps like "I get one free move" or "you can't use this special move".

If nothing else, the variety keeps things interesting.

There is a difference between balance and ignorance. Handicaps don't work very well if one player has stronger fundamentals than the other. It'll just be a slippery slope of stacking handicaps until one player ragequits. Instead of trying to Harrison Bergeron the situation, your best bet is to just play a different game or find a way to motivate the other player to learn as you did.