That's just a fanon interpretation. Her border manipulation are clearly limited, even if it is strong.
She is probably about as strong as any final boss from Touhou 6 to 8 and the fighting game bosses.
And when have we seen Yukari fighting seriously? Even as a Phantasm Boss, she just used Ran's attacks basically. I doubt Yukari's serious attacks are just clones of Ran's. I mean, why would she have put the effort into fighting seriously in PCB if she was fighting to avoid putting the effort into fixing the border instead?
Yes, it's limited. She can't go to the moon willy-nilly. But that doesn't mean she can't gap to anywhere on
Earth. And for all we know she can't go to the moon because someone interferes with her tying to do so, like the Sisters, who are equally, if not moreso, hax. It's implied she can even manipulate the border of life and death viva her spellcard names, manipulating winning and losing is nothing compared to that.
And we know she has the power to take MULTIPLE youkai to the moon, albeit, on the full moon only.
Just because there are limitations doesn't mean they are relevant if the limits are stupidly high.
If you are suggesting that Yukari is actually on par with Remilia in terms of power, or Yuyuko, when she can use her border manipulation to achieve the exact same as those two and so, so much more... I'll have to say you're wrong. Not to mention she's far smarter than Remilia at least, and likely Yuyuko too.
Really the only ones who could fight Yukari if she was serious are the gods, such as Suwako and Kanako, because they are well... gods, Yuugi due to her 'supernatural control' and, as stated in canon, Shikieiki, who is stated to have no problem with Reimu, Yukari and Yuyuko at ONCE if she fought seriously.
Of course, that's the issue. Yukari being serious. Being so lazy she'd probably never fight seriously unless Gensokyo itself was at stake.