I think that Tahm's thing is more like being a sleazy moneylender who takes more than gives. Once people make a contract with him, they are no longer masters of their fate. The Piltover lady somehow was unable to make great inventions by herself: she kept needing Tahm's help to do so and he knew when to come with the new offer. Lars entered a massive losestreak mostly because he **could not stop **: I think Tahm influenced this greatly. Thr gambler, despite his fortune and wealth could not stop Tahm from eating everything because he _ owed_ him - he let him in and gave him the power to overwhelm every people (including guards) present in the wedding.
He's more like Evelynn than we think.
I wouldn't say that. Evelynn goes after happy people, people who feel like they have everything in their life. She obviously has a preference for victims who find their happiness not in wealth and materialistic stuff, but in their loved ones: so she could torture them all in front of each other and enjoy their misery.
Tahm is attracted to desperate and miserable people or the people who think they deserve more than they currently have. He goes after greedy, envious, down-on-their luck folk and then makes them happy...until he comes again to collect the debts and take away everything. He feeds on people being dependent on him right till the end.