Snorlax and Porygon2 are certainly not necessary on all teams. Offensive teams can pretty much set up Rocks and other hazards and just force Chandelure out with faster mons to render it useless after 1 switch-in. There are plenty of offensive checks, too, such as your own Chandelure (one reason to go max Speed Chandelure), Arcanine, Houndoom, Flygon, Kingdra, Suicune, Rhyperior, etc. I can certainly find worse offenders of restrictions on teambuilding than Chandelure.
Chandelure to me is analogous to Nidoqueen in RU for me; it packs a huge punch and is immediately threatening, but the metagame has sufficient amount of resources to handle said threat without overly limiting teambuilding options. Except, Nidoqueen in RU is far worse than Chandelure in UU.
Except the switch-ins your proposing require another pokemon to be sacked in the process, or are good for one time only.
I'll break this down a bit because I don't think people are giving this much thought at all. So a few things...
Firstly, SR DOES NOT PREVENT CHANDELURE FROM DOING IT'S JOB! Now I'm sorry I had to resort to all caps to write that, but it'd be nice if people realised this. The phrase you are looking for is that SR LIMITS the number of times chandelure can perform the job it is most well known for, which is blowing big gaping holes in teams. W/out a pursuit user, that at least gives chandelure 4 times to wreak havoc, possibly 5 depending on HP evs/ivs/did it come in before SR went up?
Secondly, lets have a look at some of the offensive/defensive checks you and others have listed here, and I'll try and explain why I would not be convinced that it is a counter-argument. For reference, chandelure's attacks will be argued from the view point of a neutral nature, and either as choice specs, or not choice specs (all other sets, i'll exclude LO for the time being here). Also, for non-specs sets, consider them having forced something out into one of your checks and being either scarfed or having put up a sub, as these are the two most common sets chandy will run if not with specs
-Kingdra (0HP, 4SpD): is 2HKO'd by shadow ball on the switch by non-specs lure. Is potentially OHKO'd by specs lure if SR is up (requires very high damage roll though)
-Flygon (0hp, 4SpD): is 2HKO'd by shadow ball on the switch by non-specs. Potentially OHKO'd by specs if SR up (high damage roll required). Can only switch into specs Fire blast safely once. Depending on damage rolls, the same may apply to other sets if SR is up
-Rhyperior (248hp, 244SpD): I will pay this for non-specs sets if energy ball is not run. is 2HKO'd by HP fighting/Shadow ball on the switch by specs (may avoid this if calm natured, I used adamant nature as per the on-site analysis)
-Arcanine (0hp, 4SpD): OHKO'd by shadow ball after SR by the specs set, 2hko'd by fire blast if ability is not flash fire. 2HKO'd by shadow ball from non-specs, also possibly by fire blast if SR is up.
-Suicune (252HP, 4SpD): Non specs can only potentially 2HKO with energy ball and if SR is up. Specs can 2HKO with shadow ball depending on damage rolls and SR being up. Offensive set would be even more hard pressed than crocune and only have one safe switch.
-Houndoom (0hp, 0SpD): OHKO'd by specs lure HP fighting regardless of SR, 2HKO'd by shadow ball if you mispredict with the pursuit/sucker punch mind game. OHKO'd potentially after SR by HP fighting from non-specs sets.
-Umbreon (252hp, 252SpD+): can be 2HKO'd by fire blast on the switch unless you use protect (specs) and gone if switching in on SR, unless you use protect. Walls everything else though, so a reasonable choice.
I haven't bothered to calculate for snorlax or P2 as they have both been proven to wall chandelure unless messed with by trick, or if flame body specs for P2. I'm also not bothering with either specially defensive milotic/specially defensive arcanine as suggested by godsend as they are either niche pokemon solely for chandelure, or outclassed in such a role.
Also a side note: Can someone tell me how to do spoiler tags? I'd post calcs but this post is already pretty big right now.
Basically, the short version of the problem with chandelure is that due to it's sky high SpA, anything not named P2 or Snorlax that cannot outrun 80 base speed timid becomes a potentially large liability to carry.
One final edit, I hope: Actually I will say that of the suspects, I would've had mienshao as suspect, since thanks to U-turn + regenerator it actually has no strict counters, and only 3/4 reasonably safe checks in sableye, crobat, and maybe slowbro/amoongus