
I'm surprised that the top review of this weakness calls it very mild. I consider it way worse than average. It's probably not the worst weakness in the game (Overzealous exists, and I'm no fan of Amnesia) but it's quite bad.
Now, you might argue that Indebted has two things going for it. First, it only takes away two resources. That doesn't seem too bad. A run-of-the-mill weakness like Haunted or Chronophobia probably takes away two actions (actions being more valuable than resources), and something like Paranoia has the potential to take away a lot more than two resources. Second, you'll obviously never draw Indebted, so it won't cost you a card as other weaknesses do. And if you're Indebted, your odds of drawing any other specific card you want in your deck are ever so slightly higher.
But I still consider this weakness terrible. First: it hits you every single game. There are no reprieves. A good rule of thumb is that a standard scenario lasts about ~12 turns, all things considered. There are 28 or more cards in your deck after your opening hand. That means that as long as you're not spending a ton of actions drawing cards, there is a pretty decent chance you will never draw your basic weakness. Or, if you do draw it, you might draw it so late in the game that it doesn't matter (there are many weaknesses that can simply be shrugged off if drawn late enough). This will never be the case with Indebted, which will always hurt you.
Second, the cost of two resources may not seem that bad, but in fact they are more significant than they seem, because resources are at their most valuable on turn 1. Almost every investigator needs to play key assets to be effective, and needs to get them out ASAP. Wendy wants Leo De Luca and Fire Axe. Daisy wants Old Book of Lore and Dr. Milan Christopher. Agnes wants Shrivelling and Peter Sylvestre (and probably many other things besides.) Notice how all these investigators want cards that combined cost 6+ resources. Notice also how many of these cards grant lasting benefits and are therefore weaker the later they are played. Being Indebted makes these starts agonizingly slow. Unless you are lucky enough to draw Emergency Cache and the key assets in question, you'll have to choose between spending multiple "take a resource" actions (which slows you down a lot) or not getting your critical assets out for several turns (which also slows you down a lot.) You'll be faced with this every single game. On the first turn, resources are almost as important as actions, and Indebted costs you two. Every time.
You might say "just build your deck with Indebted in mind." Well, first, investigators are just flat-out less effective without their key assets, so avoiding some of your investigator's most powerful cards to play around your weakness is not a great solution. Moreover, by the rulebook you get your weakness after building your deck. So this is not really an option.
There may be some investigators who might not care too much about it, like Dark Horse Pete (though I think even he finds it a little irritating.) But by and large, this is a really harsh weakness.