I think you do not get the point here, mathematically the difficulty is the same for both small and bigger deposit.
Here is simple example for 5x wagering requirement for $20 and $200 deposit: For $20 deposit, you need to wager $100 and for the $200 deposit, you need to wager $1,000.
By logic and by math, wagering $100 starting with $20 is equal to wagering $1,000 starting with $200 and the expected lose is also equal in terms of percentage (not in amount).
Let's say the scenario or calculation as you say.
Let's say we deposit $20 and get a 5x wagering requirement so we have to wager $100, but we find it difficult to reach a $100 wagering requirement and even all that $20 is used up before we can reach a $100 wager.
How can we withdraw the money if all our money is gone?
But if our bankroll is greater than $100 or even $1,000, maybe it won't be difficult to reach the bet because we have a large bankroll.
Maybe I don't understand the mathematical difficulty, so I think it's simple.
Usually, a wagering requirement comes with the promotions so maybe it is better not to chase the promotions and check the requirement first before applying.
^This is a very important factor when using any casino, don't forget to read TOS before anything else even though they offer bonuses, because gambling casino does not offer bonuses that don't have a wagering requirement. This can help to prevent any misunderstandings or difficulties when trying to withdraw winnings. Because some casinos may have higher wagering requirements than others, and it is up to the player to decide what is reasonable for them.
Reading the ToS is a recommendation required by every gambler to understand the rules in each casino.
The casinos have different rules so we need to adjust to the rules and try to follow them so we don't experience difficulties later.
If the promotion from the casino does not require betting requirements, we can participate in it, but if not, we should think again about participating in the promotion and always adjust it according to our balance.
Thus we won't complain when we find out that casinos have high wagering requirements because we know it before.