You don't really need legendaries to have a good team (and most of the time you're better off without legendaries).
The best legendary available is Mewtwo, with its insane spc. attack value that isn't compromised by horrible defense and HP stats (unlike alakazam). Suicune is also a good investment, especially if you don't have the means to obtain a Blastoise. However, since you already have a Feraligatr, you don't really need another water pokemon. Furret is a pretty solid pokemon with the option (if I'm not mistaken) for a defense curl/rollout combo. Pidgeot isn't the greatest pokemon, and I'd suggest switching her out for a ground/fire/rock/steel/dragon pokemon. To give balance to your team, you need a fast sweeper such as Dragonite (who, btw, totally rules), Alakazam (who would need to be supported by massive defense boosts and a reflect setup, but dominates with its speed and great spc. attack stats), Arcanine (not spectacular, but I'm biased towards him), or other powerful pokemon (either attack or spc attack or both) with either a first strike move (quick attack, mach punch, extremespeed, etc.) or 80% percentile speed (approx rank 15+).
Red gyarados can be your offensive powerhouse if you choose not to include tyranitar or dragonite (or similar such pokemon) or decide to use those are standard balanced attackers. This means giving gyarados damage attacks over accurate ones (although stay away from blizzard type attacks that have 70% accuracy or less). A nice suicidal set could be . The good thing with this set is it allows Ampharos to be taught thunder as rainy day will boost accuracy. However, I don't particularly like on account of STAB thunder being used against you for a 120damage x 6 blow of hurt.
Feraligatr is a nicely balanced pokemon, so teach a few solid moves (surf = full of win, earthquake = full of win [but don't overdo it overall with surf and earthquake in your team]) and a few support moves (confuse ray or thunder wave type) for stat infliction or parastat infliction.
Ampharos is also solid, but slightly lopsided in terms of stats. For her, thunder wave = full of win, while thunderbolt is always a good investment. If you pack rainy day on either Feraligatr or Gyarados, thunder might be worth your while too. The main problem with ampharos is her small movepool diversity in terms of damage type, so look to also use her as support, setting up light screen as necessary.
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