I dunno, Glaceon's been working out very well for me so far in my main run. Hail + Blizzard is a beautiful combo, even resisted it's a decent chunk of damage. Really, it comes to personal preference and if it means using lower tiered mons, well, there's that. Besides, tiers should ONLY matter in a PvP competitive setting, not in a regular game where the needs are different.
And yeah, TM's can affect a mon's usefulness, though it's moreso those who rely on them who suffer.
Ultimately, a smart strategy is FAR more important then the Mons you use. If that were not the case, then literally all mono-type runs would be impossible as eventually you would run into someone who hard-counters you (Kiki for Ice/Rock/Steel, Corey for Grass/Fairy...)