Porygon2 does need Aromatherapy. This way you can recklessly charge in a t-wave / toxic / burn your other wouldn't enjoy.
You can do that anyway to some extent if you've scouted your opponents team - just switch in on the opponents Blissey/Celebi/Starmie/Roserade, trace Natural Cure and take it from there. Obviously it's no Aromatherapy but beggers can't be choosers. Quite important to note because Porygon2 is a Toxic magnet.
The thing that always bugged me about using Porygon2 is which 'filler attack' to use. Ice Beam/Thunderbolt/Recover pretty much pick themselves but then you have a tough decision to make. Thunder Wave is too predictable, Toxic gives Steels a free switch and Tri Attack doesn't have the power or coverage to justify it's use without significant SpA investment. The other options (Magic Coat, Shadow Ball, Trick etc) are too situational. I suppose Hidden Power Fire is the best shot at the moment - deals with Scizor who could normally switch in all day long, stops Forry from setting up entry hazards on you, makes sure Luke doesn't get a free SD, 3HKOs Metagross and still allows you to revenge kill Magnezone efficiently. Problem is you're left with three unSTAB'd attacks coming off a humble 255 SpA. I realise you addressed a lot of this in the OP, I'm just thinking out loud.
That said, very nice OP, I like the format. I think you're playing him up just a touch though. I've used him a lot and I do appreciate his niches but...
- Yeah, he counters Gyarados very well but a few other Pokes can stand up quite well too whilst inarguably bringing more to the team (Vaporeon, Celebi, a defensive Gyarados of your own etc).
- He does quite well against half of the Salamences out there (DD is on 50.9% of Salamence but I always found that the higher up the ladder I went the more MixMences I saw but that's obviously unfounded and probably outdated). He still isn't all that though because +0 LO Outrage still does up to 72% so if Porygon2 isn't at full health (and lets face it, he's relied on to check so many things that he probably won't be when you reach the stage of game where 'Mence will typically DD- like the analysis says
'Unfortunately, its versatility leads to a downfall: it can be tailored to do anything, but as we all know from real life, multi-tasking is hard, and Porygon2 finds it hard as well.') he can still run into difficulty.
- And fair enough - he can come in on Heatran and Jolteon very well but they can also come in on with similar ease and they are far more dangerous than he is.
Useful Pokemon for sure and I do give him brief consideration when I'm making a team but there's always a Poke that can do a similar job whilst supporting the team more effectively. Most of the time a bulky water with HP Electric can counter/check similar things. Porygon2's cool if for whatever reason I can't squeeze in a bulky water but lack of resistances (like they say, resistances are more important that defenses in DPPt), lacking movepool, low damage output and one-dimensional, predictable nature are usually enough to put me off him.
