If Protoss units ever lose “innate shield regen” there should be an upgrade to get it back
Asamu has actually suggested that in some of my IRL conversations with him (brother). The reason he gave involves Protoss harassment in PvT. There is a gap before Medivacs come online or before mech builds up enough Tanks or other heavy units where Protoss has a significant edge, specifically because the Protoss units heal while the Terran units either can’t heal or need to pull workers to do it.
Delaying passive shield regeneration with an upgrade weakens that advantage against Terran, which means you can buff the stats on Protoss Gateway units.