I mentioned it a while back and yeah, it's getting a bit crazy. There's like 4 exclusive deals, at least two which offer a customization bonus. One is this gold stubbed backpack, another is a full track suit set.
And yes:
1. it's all cosmetic.
2. personally I think don't look that great.
3. they've had preorder bonuses before.
But:
1 & 2. Sure it's all cosmetic and they don't look good... but what if they did look good and I wanted both? Right now it's "fine", but if this becomes common practice there may come a time when they start offering really good stuff as pre-orders and you're forced to give one up. There's no guarantee these items are in the game without the pre-order, if so then fine no problem pick the one you want early, but rarely a pre-order bonus is like this (if it is offered later it's usually via DLC, but if Pokemon starts offering clothing DLC for money I would want more interesting stuff then this and would have to be worth it).
3. They've had them before but not this many. There's are at least four I know of and if you want them all you'd have to pre-order the game four times: The gold backpack, the track suit set, the early Tyranitar/Deino Raid Battle, and offer of a dozen Poke Balls from the start. I got to pick and choose ONE of these. "Well obviously the clothing is the best option". Yes, but in addition to my above argument about the problem being two clothing pre-orders there's also the issue of if you're living someplace that one or two of these options aren't available? What if you wanted the track suit but you don't live near the store that's exclusively selling it? Oh well, tough luck, how dare you like a pre-order bonus you have no way of getting, pick one of the "lesser" ones in your eyes.
Also the early Tyranitar/Deino Raid Battle has be particularly annoyed because something like that would normally have been an early Wi-Fi event like the Speed Boost Torchic in XY, the Shiny Beldum in ORAS, Snorlaxium Z Munchlax in SM, or the Dusk Rockruff in USUM. I didn't need to pre-order anything to get those, I just had to buy the game when it came out and was awarded with a cool Pokemon to start my journey with. And while they may still do this with another Pokemon, it probably won't be a pseudo Legendary basic stage.
Also slippery slope argument again: sure, you can get a Larvitar and Deino later, but then in a future game they may give out a Pokemon you can't catch till post game and maybe even later give out a Pokemon you can't get period without transferring it from a past game (or getting it from the GTS). And if that's on top of there being multiple offers for exclusive clothing options you may not be able to get in the game otherwise: do you take the cosmetic or the one that gives you an in-game advantage?
"You're being a doom sayer! All of this stuff is in the game and all these pre-orders are doing is giving you early access. GF have been so opposed to DLC and pre-order exclusive bonuses they wouldn't do any of the above things said"
We also said they wouldn't do a culling of Pokemon and here we are with Dexit and no more Mega Evolutions (and Z-Moves). And this may be true right now, but Game Freak and the Pokemon Company are still a business and we've seen businesses liking to push their limits to see how much they can get away with to make money. As fans it's our duty to push back when they go to far... though it is feeling that's working less and less...
I'd like to expand a little bit about the point you made about "it's just cosmetic" (otherwise, I wholeheartedly agree with the rest of your post, and I concur on the fact that we are in a needle on the coffin situation).
Pokemon has probably always been and RPG, as it revolves around creating YOUR OWN team, that YOU identify with, on your own adventure that will differ in terms of unique moments, turning points, etc... from everyone else's.
With character customization (which was long overdue), we have expanded on the aforementioned idea. But part of RPGs, and an integral one I might add, is how cool you look and you cool you are when experiencing your adventure. In RPGs, I would argue from my perspective cosmetics are not "just cosmetics". One of the coolest things I had to aim for in USUM is the dojo karate outfit, rewarded upon dex completion.
All in all, it's a little issue, but when faced with all other borderline lackadaisical stuff we have had to put on in the last weeks it really feels like a "let's try to squeeze as much money as we can and see with how much we can get away with" situation.
I would mention that while those were tecnically unique gifts that you weren't able to get in other ways (you could breed some of those but wouldn't be in the Cherish Ball), the raid Larvi/Deino have nothing special other than being available earlier than normally in the game.
Again, I don't really see the fuss about preorder bonus. It's stuff companies have been doing for a decade, Pokemon isn't exactly the first, and I don't really see any issue in it.
After all, the main reason to give a preorder bonus is to incentivize people to preorder a game that you don't know the content of yet, rather than wait to see if you liked it or not.
Your last point is something I feel is worth discussing about. Why would you purchase a game you are skeptical about? Or, maybe, the right question could be, "why a developer has to encourage early purchases? Maybe they fear turnover tanking after reviews?" Now, this is a point of contention, but in the current situation it raises (and should raise) more than an eyebrow.
In recent years in the gaming industry we have had a plethora of broken promises, scammy microtransaction based game development, and under-achievements/under-deliveries.
In such a state (and it pains me more than I can express to talk about a pokemon game in these terms) throwing preorder bonuses left and right to an audience that is growing wearier by the day is not exactly brilliant PR.
Usually, preorders are looked at as a tool to either (or both) boost expectations or get early revenues (especially important in case of financially troubling periods, something I'd reckon we are not dealing with here, in all likelihood).
However, given the recent letdowns in much-hyped games, the general gaming audience has turned a critical eye to preorder bonuses, as such features have sometimes been associated with games that underdeliver, and you know what practice is best for marketing a game that could possibly tank? To suck people in with time (or exclusive) -based rewards, so that once the reviews are out, part of the audience has already purchased their copies.
Now, as someone who writes business plans as part of his job, I fully understand the value of early revenues and anticipated turnover that can ultimately also boost future content, don't get me wrong. It's a valid argument but a franchise with so much goodwill as Pokemon can use this to a way better extent.
Not to say that there aren't great games with preorders and exclusives, because there really are (or that preorders can be marketed way better than this), but you can see that due to 1) general state of gaming and 2) Dexit and 1-game-per-year statements, people are looking at this with a skeptical eye.
Just have a look at CD Project Red's message on whether you should preorder Cyberpunk 2077 or not to see how you can leverage goodwill to an engaged fanbase: it is blatantly stated that preorders are a huge help for them, but they also clearly say that, should you wait for reviews before spending your hard-earned money, they fully understand.