... on perhaps one or two hot-button issues. You won't find any "representative" which actually represents you on more than a few issues (at best), so voters have to prioritize—and then the winners go on to vote on their constituents' behalf on many other issues which weren't major talking points during the elections, in effect representing only themselves.
You're right that this isn't different from (almost) any other issue. It's a real problem for any issue that isn't right at the top of the priority list.
If there are 5-10 parties then there is usually at least a neighboring party that you can switch to if your pet issue isn’t correctly handled by the party you regularly vote for. It’s also a lot easier to steer the opinion of a 10-15% party than a 50% party (with the obvious downside that even if the 10% party forms a government, it will be a coalition where it only has 1:5 weight)
Any party you choose is going to vote against you interests in some area, abusing your endorsement to back policies you disagree with. The ability to switch to another party which represents you even less apart from one "pet issue" which might not be your highest priority doesn't change that.