Is your primary complaint the use of the word "kaiju" to describe "silly big monster?"
I am glad you brought up Smaug. Smaug slaughtered an entire kingdom of dwarves full of warriors of rather incredible prowess and with the best and heaviest of armor and arms. He did this without worry or concern. Further, Bard was exceptional, possible superhuman (his shot on Smaug shows so) with his archery and placed an, if not magical certainly exceptional, arrow in a single small chink in Smaug's armor, at distance, while Smaug was flying and burning Laketown. A hole that let the arrow pierce directly into Smaug's heart. So, absent this plot device and superhuman skill at archer and a handy magic arrow, Smaug was effectively invincible to even the best armored and equipped warriors. Let's not forget that the previous Lord of Laketown, himself a noted archer, used multiple Black Arrows against Smaug, hitting each time, and not penetrating Smaug's hide once.
So, if we go with D&D's dragons being like Smaug, then, yeah, it makes a lot more sense that such dragons could take on a tank just fine before we get to a human in armor with a sword walking up and doing anything at all except dying swiftly. Because we know that this was attempted, en masse, by trained and fantastically equipped dwarves, and it wasn't even a fight but a slaughter.