The games I've played with a true route had either the girl make an appearance in the final route or they were quite likeable. Example for case 1: Lunaris Filia, Sevens. The "secret" character showed up for a very, very short time on yours 2nd playthrough+, but the meat of the story = true route. Similar for Kamigakari Cross Heart (which was for 99 % light-hearted, though
).
Example 2: I think more common à la Suzukaze (<3), and other whirlpool-VNs that are not Lunaris Filia and Sevens. Or Ryuukou no Melodia which's true route is a rare 2-girl harem
The only case where the "true route" could have been better romance-wise was Concerto Note. It just didn't "click" for me as with other cases. And the horrible Grand Ending of Kamidere and its harem end. I consider it still as a poor excuse to add one h-scene for the sub girls + group-up.
Long story short: Overall, I consider myself fortunate that 99 % of the true routes where you end up with a girl, were done well enough. Obviously it helps that I'm easy to satisfy VN-wise and try hard to stick within my genres non-darkish, (gory/bloody) VNs
.