I wasn't trying to make out his pivot to be an unbeatable, OMGWTFHAX type move, either. I'm just saying that between his pivot grab, his ETS, and his up smash, it's a little difficult for Jigglypuff to effectively space back airs against him.
For instance, if she deliberately tried to fake me out in order to bait a counter, I can more often than not ETS back a ways instead of attacking, which opens up some movement and attack options for me.
Coming in high tends to be risky because of Yoshi's up smash, and her Pound is also something to be reconsidered for the reasons Mmac outlined.
I'm certainly not saying this is a no-win situation for Jigglypuff. There's certainly always options for every player. Even Donkey Kong has options against King DeDeDe. For me, it's a matter of risk assessment. Who is more likely to come out on top, given all of the possible variations on a scenario as well as what coming out on top nets that character in terms of damage and positioning.
For instance, say she gets a little too gutsy and tries tapping me with a back air. I see her coming in at a nice angle for it, so I go for an up smash. If Jigglypuff comes out on top, she lands a back air and puts me in a brief stun, and can either attempt to back air me again, which would put us in the same scenario, but with a diminished back air on her part, or change her angle and do something else.
Not a bad scenario, but let's look at the alternative. Say I hit the up smash. She's gotten hit with a smash attack, she's flung upwards and outwards at an angle. Now she has to start either falling down on me (which she does very slowly), or she has to move away from me. Either way it buys me time to reposition, Egg Toss her, or even attempt an up air (or fake an attempt at it). Strategically speaking, my coming out on top in this relatively even scenario has a more significant impact on the match-up.
I would put it to you that the majority of the situations in this particular match-up work this way, making it extremely difficult for Jigglypuff to get the upper hand. Again, it's not to say that she can't do so, but as they say, she has to work harder for it. When you take into account that in an approaching situation, Yoshi has better options than her (usually, though this can be context-dependent), in an up-close confrontation they have about the same number of options, and that in a KO situation, Yoshi has more potential for landing that final hit, I would say that it is mathematically weighted strongly in Yoshi's favor.
)
You ladies need to calm down. Let's wait for a writeup and then move on, it's not that serious.