Yes and no. The party has a life cleric, a bard and a paladin. This group has a crapton of healing. But, yeah, fourth attempt at a strafe. If the dragon's backing off for two rounds (or so) between runs, that gives the party a lot of time to repair damage. Take the 8th level Evoker. Probably somewhere in the neighbourhood of 40 HP (give or take) So, a failed save drops him. Ok. But, it's not enough to kill him outright. The Paladin has him back on his feet in the next round. If not the paladin, then the cleric and the bard. The fighter's got enough HP to simply eat at least one breath weapon, and quite possibly two.
You don't start healing from your negative amount, you heal from 0, so, the paladin LOH is worth 40 single round which puts our wizard back to full from negatives at least once. Both the cleric and the bard have 4th level spells. That means at least 1 death ward (or should) which keeps the wizard up. Command spells readied at 60 foot range to "Grovel" make the dragon thud into the ground if it fails its save. A bevy of Cure Wound spells, you are facing a dragon after all.
IIRC, the paladin is a Oath of Vengeance paladin right? (I can't be asked to look it up). Abjure Enemy, range 60 feet makes the dragon go thud on a failed save or 1/2 speed on a success. That nicely keeps Mr. Dragon in range of javelins for a couple of rounds, even on success.
IOW, there are a ton of options available to this party besides flying the paladin. Now, apparently I missed that the paladin had a dragon slaying sword, so, my bad. I was going on the basis of a fairly standard party. Which isn't to say that flying the paladin isn't an option. Of course it is. And a pretty good one at that. But, it's hardly the only option available. It's not like the party is completely screwed if it lacks a Fly spell or a bevy of ranged fighters. The party is still perfectly effective on the ground. It might take a bit longer, but, meh, not that big of a deal.
The fighter did not have a dragonslaying sword at the time. You're reading one party that I responded about at 15th level and one party that was 8th level and mixing them up.
Why do you think the party has all these rounds? The paladin had to use LOH on himself after getting smashed on by the dragon. The entire lair was difficult terrain.
All these other options require saving throws. Why do you think the dragon will miss them easily? Or not use LR to resist? If they fail, then what? The dragon is far ahead on damage. You're going to get hammered. You keep listing these abilities as though we have unlimited time to hammer the dragon, pound through its LR, and keep on trying other tactics.
We have about three rounds to get it engaged and do substantial damage. It will as you stated kill the wizard outright on a failed save. The cleric is nearly dead to. You seem to be forgetting that the dragon gets to breathe, legendary action, and lair action. So breath weapon, shrouding obscuring mist that does damage, and tail slaps. It killed two party members with the damaging mist because we couldn't see them to heal them, yet the dragon could see in the mist to hammer us.
You keep listing character abilities as though the dragon is doing nothing while this occurring. You don't take into account its DPR with all its actions. You don't take into account that even one made save that doesn't require LR is advantage dragon. Your listed tactics would not work the majority of the time, probably in the 90% plus. I'd love to run this encounter with you on an actual mat in the lair we were in the dragon actively looking to kill your weakest members if they show their face ignoring the paladin and fighter as they take a round of hits from them to completely eliminate the bard or wizard from battle or just slow them down with the obscuring miss and rip apart the weaker members.
The stuff you're tossing out does not work as well as fly. It is purely experimental with no high chance of success. In fact, using your listed tactics is an extremely high chance of death. There are not a ton of options. Everything you listed is easily countered by the standard capabilities of the dragon. The only way your list of tactics has any chance of succeeding is if we had a lot of time to try them pounding through LR.