About your ideas:
- never replace Aegislash!! He´s one of the best mons you can have in-game. You could consider switching between this special one in doubles and a sacred sword, shadow sneak, king´s shield, swords dance Aegislash in single battles.
- entry hazards one greninja are not useful in-game. You should add Ice Beam as soon as it´s available, however.
- Blaziken: a 120 attack without boosting item and a 85 base power move are most certainly not enough to "one shot anything anyway". Blaziken one the other hand DOES get one shot by basically any special attack (and any physical attack before boosting with bulk up). That´s why Flare Blitz is the safer option: Getting three kills consistently is better than sometime getting six, but most of the time getting one.
- Garchomp is a little tricky. Until you get Earthquake, the defensive set is the only one that´s really viable. Once you get Earthquake, an offensive one with a z-Crystal (dragonium or groundium) and Swords Dance should be a lot better.