What 5dB peak at 4.5kHz? There is a gradual rise in HF around 5kHz peaking 5dB at 14kHz. Padding the tweeter down a couple of dB would probably be the most one would want to do to tame the HF energy a bit. I can understand why AJ chose to voice the tower a bit hot since its so short and the listener will typically have their ear level higher than the speaker. Also in this price point, most people shop for boom and sizzle at department stores.
One would have to look into it closely, it seems there are two defined peaks. I'm very suspicious that there is a break up mode peak from the woofers involved in the first peak.
This would explain the reports of not liking them pushed hard. I suspect the tweeter is being cut off early to try and minimize the situation and this is why you have the second output rise. I'm guessing here but these are my suspicions.
If there is indeed a rising response from the woofer and it where dealt with then the tweeter could be crossed lower and padded down correctly and the response would be better over all. The two humped camel type pattern in the response is what makes me suspicious that the root cause here actually lies with the woofer.
Afterlife 2 was having a lot of trouble with disc reproduction with these speakers before he lost them to Hurricane Sandy. He was complaining bitterly of sibilance I thought may be he had a cartridge loading problem. I made him cables of varying capacitance, but it did not help. I now realize the cause of his problem.
I put together a system with JW 4" full range drivers. My final version of the Mark II driver before going on to the Mk 3. These speakers are not sibilant, but do not lack sparkle. He his over the moon with this system. So it really took a change of speakers to solve his problem. This original design is over 50 years old! His speakers are about 40 years old.
So even though these Pioneers are at a very affordable price, I would say they need recommending with caution in their present form. I think I would likely find them very irritating and be happier listening to a old table radio.