Seas metal domes are very good. Aluminum is a better choice for dome material IMO compared to titanium. Most of the time the aluminum is alloyed with other metals and depending on the specific alloy used, it typically has better internal damping than titanium and results in a lower breakup peak. I've seen some titanium domes with 15+ dB peaks. JBL had that titanium dome with embossing like many compression driver diaphragms have. I don't think that does anything to reduce the HF breakup peak though.
I came across some OE crossovers that had a notch filter section just to attenuate the sharp ultrasonic peak from the tweeter. I've tried this before on my own designs and didn't hear a significant difference. Unless you have equipment capable of measuring this peak, its just a speculation as to whether the correct frequency and amplitude was chosen to get an accurate result.