I use Pidgeot exclusively as my mega. I've been wanting this for a long time. Outside of theorymon, I dont get any of the arguments here. I've used Pidgeot in RU,UU and OU and while its good in those tiers, it doesn't really do anything but fire off no miss hurricanes. The hax is not guaranteed as some days I would get it and other days I wont, like hoping for burn on physical attackers. The confusion is good when I can land it but there is still a chance it does nothing at all.
I have played many m-pidgeot sets and by far the best set I found involved hurricane, heatwave, u-turn and filler because when I tried to use the wall breaker set, I could not use it in most the games I played and ended up clicking hurricane anyway. The one game I managed to get it to work was when a blissey decided to stay in and let me setup. Against other team, I just never had the chance to use it unless a very specific situation popped up where I could click workup. On top of that, unless the pokemon is really frail, its not going down in two hits most likely.
Even if I did manage to get the +1, something would switch in and force me out, fearing the scarf or just going down. Jolteon is very fast, m-beedrill gets the OHKO with poison jab after rocks, any scarf attackers with at least 65 bs in speed with nature will outspeed max speed super bird and more than likely get the KO. Scarfed pokes are very common. Other mega like beedrill, sceptile and aero are not scared of pidgeot after they mega. Other defensive megas like amphy and aggron and others tank the hits. Sure they have to worry about confusion, like physical attackers have to worry about burn but no Pidgeot is staying in to fish for the confusion if the pidgeot player can avoid it. The only time I had to stay it was because I had to but ended up losing my pidgeot most of the time.
Pidgeot's speed tier is decent but its far from good but there are a ton of faster threat, with or without a scarf that deal with it. Like said above, pidgeot has switch ins that can force it out and I understand the counter can be confused but this is no different than switching into any other attack where you eat a crit, take some kind of status or stat reduction. This is just the risk of making defensive switches.
Also keep in mind Mega Pidgeot doesn't have the best bulk to begin with. Almost any hit from an attacker will take it down. Bulky defense rotoms deal about 70% with volt switch.
0 SpA Rotom-W Volt Switch vs. 4 HP / 0 SpD Mega Pidgeot: 188-224 (61 - 72.7%) -- guaranteed 2HKO
Hurricane against it is almost a 5HKO
252 SpA Mega Pidgeot Hurricane vs. 252 HP / 212+ SpD Rotom-W: 66-78 (21.7 - 25.6%) -- possible 5HKO after Leftovers recovery
Most other hits from full (non super effective) deal about 75 to 80% to mega burd so if it takes any rocks damage, there is a good chance its going down to any attacker. To put this into perspective, most bulky attackers with non super effective can deal damage you can't roost of effectively
252+ SpA Florges Moonblast vs. 4 HP / 0 SpD Mega Pidgeot: 186-219 (60.3 - 71.1%) -- guaranteed 2HKO
Not sure what other info to post but based on my own personal experience (and have some recordings to prove it) Mega Pidgeot is not broken like people say it is but it can be VERY good once its checks have been dealt with but if you want to be honest with yourself, what isn't.