I believe most discrete ESD devices protecting multiple pins in a single package & ESD test standard such as IEC 61000-4-2 has one FATAL flaw, they test one pin at a time (and pass, of course), but in reality what will happen if hands touch more than one pin? If ESD energy is too strong, the single ESD protection can't handle mutiple pins and would fail. Second flaw for discrete ESD protection device is their clamping voltage (greater than 6V or even more than 10V, very common) usually is way MUCH MUCH higher than normal standard 3.3V/1.8V, etc Vcc/Vdd working voltage, at this case, then how could it potect DUT? (of course better than none, at least these discrete ESD protection device already absorb most ESD energy if not all). Based on this, still room to improve.