Wagering requirement on deposit before withdrawal is actually standard rule and I'm sure most casino implement similar rule.
The difference is about the number, most other casinos implement 1-2x wagering requirement on every deposit but trustdice 5x for 1st deposit only.
Your opinion is the best possible thing to do to complete the wagering requirement and maybe it is the most used strategy when it comes to such rule.
Since the rule at Trustdice is applied for 1st deposit only, the best option for gamblers who want to deposit big amount then better to make small deposit for the 1st time then gamblers can do bigger deposit later.
On gambling sites there must be a requirement for a wager if there is no wager requirement then it might be considered as mixer and it will increase money laundering and other unethical events. But the 5x requirement is unfair while there is no bonus received for that 5x requirement. If it was for a bonus then there would be no issue.