Siglut I think your points are valid that blaziken eases the prediction against skarmory a little bit and doesn't waste a moveslot to reduce the unreliability of focus punch.
I think for me what charizard has going for it is the ability to pivot effortlessly into metagross and gengar. Switching into metagross twice for free is not something most offensive pokemon can do. Gengars tbolt also brings charizard reliably into blaze range, whereas with blaziken there is an awkward situation where tbolt brings it down after some spikes but not quite down if you get what I mean.
There are teams that zard is going to do better than Blaziken on, but I think they are pretty limited in number. It definitely requires a team that has solid defensive synergy already, as it provides next to nothing in that regard,
So I completely disagree with this because as you mentioned, zard has one time defensive utility but that is sometimes all that offensive teams need. Gengar and metagross are not easy mons to pivot into for offensive teams, but offensive teams also dont need to take that many hits from them too. As for the inability to handle tar, i tend to like using Dugtrio with zard.
I also think the importance of having ground immunes on offense teams is understated. Many offensive teams are completely wrecked by Dugtrio, so having something like zard that can sub up on a dugtrio ko and unleash something devastating is quite important. On the other hand, blaziken is dug weak, so then you might have to support it with other dug lures or abusers. By using zard over ken, you turn a dug weak into a dug abuse.
The zard set that I prefer (mainly because i like spikeless offense) is the sub petaya set. That alleviates some of the problems you mentioned. Under sand, a fire blast to mence and an additional blaze petaya boosted one one will take it out. I think you understate the importance of being faster than most Salamence. The blaze petaya boost also lets you take out Blissey after a well-timed focus punch.
On the topic of speed, I think it cannot be overstated that there are some really important things that charizard can potentially outspeed. Slow taunt Gengar, Salamence as mentioned above, speed tie with Zapdos are some things you didn't mention. But outspeeding Moltres, Celebi and Jirachi are so important.
Charizard is favored to beat Moltres in a 1v1 and can even take it down with a bit of chip while switching in because of Blaze. Every bit of speed and spikes immunity matters then. Offensive teams dont have good moltres switchins otherwise, and you can end up getting forced into this situation.
Celebi and Jirachi are not just two random Pokemon zard outspeeds. They are very prevalent, and calm mind variants are very dangerous. In addition to outspeeding (most), Charizard also doesnt get 1hkoed and can make use of blaze. That means using zard instead of blaziken, you turn a weakness into a check. You can pressure celebi before it baton passes out so that it can never set up on you again, and you prevent jirachi from running over your team. Without charizard, you might have had to resort to other measures like exploding (ok you exploded the target, but celebi's still there), trading your tyranitar or metagross (but all superrachi teams are designed to have already gotten those two out of the way, or intentionally use jirachi to get rid pr them, so you might have lost them already!), or using Roar zapdos which will temporarily stop them in return for taking a huge chunk of damage.
The most recent successful team I have seen blaziken on is z0mog's blaziken breloom ttar team. If I remember correctly, tyranitar is pursuit so that helps to lure dugtrio for the breloom kill through mach punch. Blaziken needs quite a lot of support to make it work, and it's not easy to divide the matchup into dug and non dug, because dug belongs on both defensive and offensive, spikeless and spikes teams. The number of S/A ranked mons that blaziken can switch in on safely too especially under spikes is essentially one - skarmory. It needs to pivot carefully into blissey lest it gets twaved too.
Charizard in comparison switches freely into Metagross, Gengar, Jirachi, Celebi (and Dugtrio if you consider that) on top of Skarmory among the A ranked mons at least once, and it knows it will not get KOed. It also knows that if it gets into blaze range, it can make good use of its speed to make the best use of its ability, outrunning mence and perhaps some zapdos. It does not need as much support. In fact, it supports with its offensive pivoting. The strong blaze fire blast can even be preserved under Spikes, unlike Blaziken. It can play the matchup dividing game too - the stuff that truly hard walls Charizard is of a particular type of passive stall team (milotic, defensive starmie) that the rest of the team can be tailored to beat. Thats a lot more niche and checkable than straight up losing to Dugtrio. Porygon2 and dug countertrap strategies do exist but thats exactly not what versatility is about (and it's hard! There are going to be defensive holes no matter what if you take this p2/dug route, from what I have explored). The most reliable strategy that a friend and I have found with blaziken was to use it with spikes stack to exploit its switch forcing and so that dug traps are frequently momentum-losing. That has some avenue for exploration I think.
Perhaps you can share some viable teams that use blaziken? I will be interested to take a look at them.
Cheers!