Use 15s and 20s, or at least a combination of 6 Pokemon that offer many ways to max out level usage per match. With your setup, the only way to get the full 50 level limit is using both Charizard and Alakazam, which is very limiting. Not to mention 17/16/16 is a bit ehh.
It doesn't matter how you got the Pokemon, it's not a legal team for Pika Cup. Sure Pokemon Stadium will let you, but if you're going to use abnormal Pokemon, at least use good ones that you can also obtain via glitches.
If it's an illegal Pokemon or moveset, it's illegal no matter how you got it. Level 16 Venusaur definitely counts. Unless you're in-game or beating Pokemon Stadium's single player. Then you're free to do whatever you like. --- Look! There! A sig!