/u/yca_ca your first tip is helpful no matter the circumstance, but your second and third end up being less effective than they sound, given certain caveats. For 2), this is only effective if the enemy team does not bubblestrat. Once they get the bubbler in, it is GG, you have actually spent more net resources than them in the long run. As for getting the bubbler in, it is training (traditional method) 9,000 prestige worst case scenario for them, which is not hard for anyone with a decent prestiger line up. So again, net resource loss for you.

Finally, 3) is usually ineffective because anything near the top, assuming it is a decent gym, is going to have relative high CP. Which means that again, if the enemy team has a decent prestiger line up, it is hard to inconvenience them. For example, 2800+ Snorlax/Wigglytufff < 1400; 2400+ Lapeas/Electric (Raichu, Jolt, Electrabuzz) /Fire (Arcanine)/ or even Wigglytuff <1200.

The hardest this to prestige against are lower CP defenders (e.g. 1800 Lapras/Snorlax or 2K Poliwrath) but you will rarely ever see those on or near the top of a decent gym.

TLDR: "Crippling" was a gym was only really effective for inconveniencing the enemy team when the prestige mechanics were reworked to where you gained 500 prestige max, because even if you had a good prestiger line up, the numbers we be so low as to almost always need at least two