Truck-kun as a meme was spawned with 4Chan discussion after MT's popularity, but the use of vehicular accident of one form or another to initiate transfer was already common.
If you're trying to say that Zero No Tsukaima didn't have a harem in an action-fantasy setting, I don't know how deluded you are, but pass me some of what you're smoking! XD
K&M has nothing to do with MT being created, it's simply another predecessor within the Isekai genre, that continued to build and strengthen the tropes of the modern iteration of the genre that ZnT started.
There's a reason I said there's plenty of older isekai, eg. El Hazard, Rayearth, Escaflowne, Those Who Hunt Elves, Fushigi Yuugi, Inuyasha, Abenobashi, Twelve Kingdoms, Red River, even .hack//sign (I believe it was among the first virtual world isekais, along with Digimon), to name just a few, or even older with series like Crest of the Royal Family; but I actively put them aside from consideration and specifically dialed in on the modern isekai genre, instead.
Do remember that many isekai stories start as light novels or webnovels long before they get turned into manga or anime form, as well, and the transition between mediums can be asynchronous with their initial release dates; Mushoku Tensei was written starting in late 2012 until 2015, while the LN version was written from 2014-2022, and the manga started in 2014 as well and is still going. By comparison, Tsukimichi started in 2012 (It started before MT, but as it had been deleted from syosetu and moved to Alphapolis as of 2016, there are no webpages remaining there that isn't dated afterwards, eg. the notice that transfer, which initially started in 2013 as noted on Alphapolis, has finished) with its LN version started in 2013, and manga started in 2015, both running to present; this gives it the appearance, for those that just read manga, that it came out after MT, rather than before it and/or concurrently.