Lock feature is not the problem, problem is the people who are not using the feature properly, in fact misusing it. The other person always can create a shadow of the topic when they want. I think it's absolutely fine to do that.
Almost all the features in the forum have ways in which they can be misused by forum members. Take for example;
- Self moderation - Could be misused by scammers.
- Merit - Could be abused
- Bumping - By project owners to find a way to push their threads to the first page.
- Lock thread etc
In the end, every feature is vulnerable, it's just for we to learn how to deal and live with the loopholes.