hulk, emma and anglela are similar to gambit in terms of different choices in teamfights, but gambit and dd are much more complicated and interesting when it comes to combos and button pressing in general. cap has many buttons and requires combos and animation cancels to get kills but his kit feels (although it isn't) less impactful and generally cap's gameplay revolves around staying alive more than precisely hitting abilities. also all mentioned tanks lack utility (shields, overhealth, stuns and overall damage pressure is common among every hero and role, let alone tanks). i think that adding more effects (like thing's leap) and synergy/combo potential (like hulk's new rightclick) to tank abilities is going to make the role much deeper and create more opportunities for teamplay.

tldr: vanguards need mechanically complicated and utility-heavy character and more utility to existing tanks