Like I said in the other thread, Shaymin S is a good poke in OU for providing a check for Bulky Water types.
Frankly, if I manage to get a grass type in against a water type, and I have the threat of 1 hko'ing your current pokemon, I ought to be rewarded with the chance to lay out some serious pain to your team.
So yeah, if you were lame enough to let that happen, I think the fact that I have a chance to 2hko your zapdos with seed flare is quite fair,
considering that when Suicune came in and blocked my heatran (loling the damage), Surf could be brainlessly spammed to hurt anything on my team, including Shaymin S/Salamence who are already getting hurt by SR.
So yeah, compared with the power of suicune to come in, lol at heatran damage, get leftovers back up (if no sand storm), and hurt just about anything on my team with Surf, including a potential 50% hit when combined with SR against even the non-water pokes that resist it,
I think Skymin's power to get a fair chance of killing the next pokemon you switch into it with Seed Flare/Air Slash, actually quite balanced.