Commander Niall is a sort of sample platter of annoying fromsoft boss fight tropes: inescapable AoEs, nonsensical reach, bonus enemies, shoebox arena, annoying runback complete with enemies that hit you through the fog gate
The best I can say about Rykard is that he's 'less annoying than Bed of Chaos'. I think people mentally filed him under 'gimmick boss' and sort of disregarded his annoyingly long health bar, repetitive move set, and utterly nonsensical phase two attacks.
The thing that makes Rykard a truly rancid boss fight is that he insists you replace your carefully curated kit with holding l2 and r2 on one specific weapon forever in a fight that eschews such flippancy as 'positioning' or 'stamina management'. And then he asks you to do it for an inordinately long amount of time. People say you don't need to upgrade the serpent killer spear but you really do if you want to kill rykard in a normal amount of time.
and then just for funsies he makes every spirit summon useless except for the one spirit summon that is already broken and better than all other spirit summons.