I think the bosses in KOF games only start to get really hard from '99 onwards (except for Rugal in 2002, who is relatively easy). '99 was about when the game start letting you use "service mode" to make it easier, so that could be the reason.
Disagree. Although, I really think it varies from person to person, game to game.
For me, the bosses I find easiest/most manageable are: Goenitz, Krizalid, Clone Zero, Zero, Igniz and Mukai. Basically, mostly all the bosses that came at 99 onwards! Nothing to do with continues/service modes, I just found those bosses "fairer". The whole Zero/Igniz thing is easy as long as you opt for 1-to-1 ratio with the boss. You'll NEVER defeat either (esp. Igniz) if you chose 4x 1/4 ratio characters instead. Always trim down to you single best character for those 2 final encounters.
I tend to prefer the Street Fighter games (like the Alpha series), as they are much more based on fireballs and dragon punches. Dragon punches (and fireballs) are less useful in KOF, which was probably intentional on SNK's part.
The whole Fireball/Dragon Punch shit is exactly why I cannot be arsed with Street Fighter anymore, sans the III series, which had much more depth (akin to SNK's fighters) > the SF4 gameplay 'routine'.
You're right. It was intentional, and imo, it was for the best, as it makes the dynamics of the combat so much more interesting. SNK have ALWAYS been about the options and the inability to sit comfortably on Sonic Booms into Somersault, Tigers into Tiger Uppercut and Hadokens into Dragon Punch.
Fatal Fury already understood the requirement, initially met via the 'plane' system. Then, in later games like KOF, things became much more flexible, with the ability to roll/evade projectiles, run and jump near full screen distance at fireball abusers BEFORE having chance to DP and even Super Jumps and Hyper Hops too. C+D and A+B on block are extremely useful/flexible too.
SF just doesn't compete in this area, and whilst many love the simplicity, for me, I struggle with the lack of options/simplicity nowadays more than I used to...