It really just depends at what LEVEL you want to compete at.
Will you win an NBHA world championship on a 12.2 pony? No, you won't. But that may not be your goal.
If you just want to go to local fun shows and have a good time, then go for it. We have a local family who has this little pony that just SMOKES everyone at the local gaming shows; including the adults and big horses.
Ponies, in general, are going to take much tighter turns because that is where they can make up time in a pattern, since they lack the long legs on a straightaway.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.