My experience with my Blisseys is that, as soon as I put them in a gym, any gym, they are a magnet for an attack. I've tried gyms that have almost no turnover, and they almost never last more than a couple of hours.
It's like there are people out there that are deliberately taking out Blissey just to prove that they can.
I asked a similar question a few weeks ago and the advice is simply choose the pokemon closest to your aims out of the 4 'best walking value' pokemon, which are namely Chansey, Snorlax, Dratini and Larvitar. By that I mean something you need the least candy to make something 'complete' (i.e. if you already have a level 23 DT/OR Dragonite, level 24 B/SE Tyranitar etc. walk the respective mon to complete it rather than thinking of super long term projects like walking 800km for a tyranitar)
e.g. I hatched a level 20 Lick/HB snorlax and I was walking a Pupitar (I am 76 candy away). I swapped the Pupitar back to the snorlax as it is already with the best moveset and I am way closer to pulling it to something usable than with walking the Pupitar (hatched snorlax during the event at level 20 and with walking/candy from the egg, it's already at level 26 now).
Blissey is most valuable or whatever you find fun/cool it is a game.
a tower full of blissey and maybe snorlax is about the only thing that would deter me from attacking a gym if I was say at a cafe and bored for a bit it just wouldn't be worth the resources.
Snorlax tyranitar and dragonite are way cooler then blissey but Blissey is the most valuable mon in the game right now.
I agree with you for most gym scenes. In my competitive gym scene it's kind of different. Most enemy gyms are very tough often like the one you talked about. You better be able to take one down quickly and efficiently or you are getting nothing. You also need to be able to inflict punishment on the gyms your team typically owns that get those mons added to them after a takedown. If I had to struggle with junk Blissey counters I could do nothing about this. At the same time, Blissey or Pidgey, no gym is staying up long enough for you to collect.
And a good moveset Tyranitar is tougher to get than Blissey since all of her movesets function fine. I don't think most would trade a great offensive moveset Tyranitar for a Blissey in my area at least so I guess value can be relative to your area in this game.
yep on my own turf I take out any blissey before they start getting a tower on. And try to punish anyone that takes down one of my only two stable gyms.
My Blisseys don't feel special to me and I kind of wish I didn't have to walk her for ever and ever (since evolved larvitar which i got lucky on first evolve).
I was walking with high IV Eevees for a while trying to get some good Espeons and Umbreons. It was satisfying because I was constantly working towards a specific goal of 10km, but it also takes a lot of extra work tracking how far I've walked and switching to another at the right time so I don't waste too much distance.
I've been walking with my Larvitar for a while, now a Tyranitar, and it is nice to just ignore it and occasionally be surprised by a free candy.