Yeah, but at this stage of Pokes, especially with the advent of older region pokes coming in, how often would the 8th gym be a challenge anyway?Except at that point in the game it was impossible to take down Miltank before she could sweep your team with Rollout unless you were overleveled.
By the time you're at the 8th gym you should have plenty of ways to OHKO everything he can throw at you, unless the gym leader happens to have pokemon that cover his primary weaknesses. The less pokemon he has, the higher the chances he won't be able to do so.
Hell, overall, the only 8th gym I struggled with, and consider the fact that I'm absolutely HORRID at In-Game (well, I'm not much better overall in Pokemon), was Juan in Emerald, and that's just because his Kingdra was a dick.
But yeah, if people are complaining, then show how you'd build your own Eighth Gym, while going under the rules that all the pokes have to share a Typing and have to share at least one TM move of said typing (which will mostly likely be their main STAB), Levels and other things within reason as well.