The Non-nerf ways to have dealt with Harrassers being overbearing, WITHOUT maiming Valkyries.

The solution has always been rather simple. Give the Harasser the same weak area that a normal front engine vehicle would have. THE FRONT. If you want to TRULY stop them from Blitzing, that is the the most effective way to do it. This way, on approach, they are vulnerable and will not be able to stay close, not face first anyway. If their tail is the most fortified they will have no choice but to run around basically blind to their enemies movements depending strictly on their gunner to target, or risk major, if not fatal damage by trying to dog people.

The sides would be the mid-armor spot, so while yes; they will still be able to Circle Strafe, they will not be able to do so as long and will be far more inclined to turn AWAY from their enemy instead of toward them forcing a break from attack or do some distance dancing. This would put their engineer at risk, so Ru-pair would be something that could be stopped but would also add a secondary shield to their rear quarters, so an added bonus to the Car itself if it chooses to retreat. (Once you reinstate Rumble-seat Repair that is.)

And with that, the Terrible Toy car would not be able to run directly at larger vehicle and would be more so relegated to its harassment duties as opposed to a vengeful eraser.

That was the elaborate way. The EASY way is to simply make the car itself vulnerable to Splash Damage. This way even if a tank or turret misses a direct hits, unless they are running A.P., they will still be able to send them running and force them to rethink dogging and keep their distance, all while lowering the number of people who would spam A.P. in order to cheese other vehicles.

This will allow everyone to keep their Ru-pair and weaken the car's battle potential, without weakening Harasser or the Valkyrie itself.

The point behind nerfing Harassers, also applies to Valkyries. Rumble seat repairs made them nigh unstoppable with a full crew.

NIGH UNSTOPPABLE?! Please... Tell me you did not type that with a straight face? I have not met a Valkyrie that I have not been able to kill with the A.A. that is available. Even a Full Crewed Valkyrie could only accept healing from one Engineer at a time so at the most it would only benefit from two healers at a time to keep the flow constant. The rest had to be H.A. or L.A.'s to truly be a threat. C4 bombing only worked in HUGE engagements when they were blessed enough to show up under the radar. So they might get 1 vehicle kill before being ran away and then shot down, but that was it for them once anyone payed it any attention.
About the only SERIOUS threat that these things presented to their enemy was if NOBODY was looking up and everyone was on foot, or if they were in a lone vehicle without A.A. type defenses. Even a Basilisk was enough to send them running. Within the past 4 years I have encountered exactly one crew that managed to give me enough trouble that I wound up having to abandon my vehicle and let them have it; even then I came right back and challenged them again and killed them to the point that they split up and called a Liberator to help deal with me. I shot it down as well as the Valkyrie and they promptly left me the Fell alone. These things were nothing more than the literal embodiment of 'Low-hanging Fruit'.