These two may be hard, but unless you're ranking by the hardest boss in the game and not average boss difficulty, MG2 is still not that much harder than all the rest.
It is infact much harder than the rest because even the most average gaming kid can beat any of bosses in the MGS games w/o much trouble (On a normal playthrough). I don't think the same can be said for MG1 and especially MG2.
And speaking of average difficulty of bosses, I can honestly say that even the easiest boss in MG2 is tougher than the toughest boss in the MGS series. Why? Because in the MGS series, once you figure out the pattern to beat a boss, it is next to impossible to lose to them if you're playing seriously (On a normal playthrough) whereas in MG2 (And even some MG1 bosses), even if you know their pattern, you have a much higher chance to screw up because of the dated controls and mechanics. Not to mention, Black Color and Night Sight requires a fair amount of luck to beat.
And I think people over here are really undermining the MG1 bosses considering the fact that on a bad day the bad mechanics can screw you up against some of the easiest bosses.
Comparing the difficulty of MGS bosses to the MG bosses is like comparing Final Fantasy bosses to Shin Megami Tensei bosses.
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Rock n' Roll and Glam Metal... It never died