Blissey Vs Dragonite

That's not saying much because a 1600 Cloyster w/ FB/B could rip through that Dragonite. You should prob put up that Blissey in a gym as soon as possible.

Try the way around. I bet your Dragonite couldn't defeat your Blissey, however hard you try to dodge.

You shouldn't feel bad about the moveset. DG was buffed up and is now a good charge move. ZH+DG is arguably the best defensive movement on the best gym defender in the game. Some calcs/spreadsheets will suggest HB is better, but when you factor in you are far more likely to miss dodges against a DG defender than HB, and DG is super effective against the highest DPS counter to Blissey (Machamp with new moveset), then I'd consider ZH+DG to be better than ZH+HB overall as a defender.

Blissey also can work well as a generalist attacker for non-Snorlax/Blissey gym defenders that you can easily beat in 99 seconds. With a good moveset, it retains a far higher % of CP than any other mon (unless there is strong type counter on strong attacker). So you'd go through more gym defenders per revive or max potion than with anything else. However, while ZH+DG is a great defensive moveset, it's one of the 2 worst offensive movesets, probably the worst overall.

I'd also suggest at least dodging charge moves when using it as an attacker. You'll retain a tremendously higher % of CP, which is the main reason for favoring Blissey as an attacker.

Dragonite is an embarrassingly bad defender. It loses to metapod: https://www.youtube.com/watch?v=j6_9nspJ9l8