All of those things impose size limits and not just for dinosaurs. The size limit for pretty nearly every sort of thing was substantially greater in the recent past. Ten thousand years ago (by stand reckoning of time) there was a 2500 lb bear in California, a 1500 lb lion, a 700 lb beaver in Minnesota...
But the worst problem involved the necks of the diplodocids (the sauropods which held their necks outwards). For something like a seismosaur, you could easily be looking at a neck which was 50+ ft. long and weighed 50,000 lbs. If the center of gravity of that neck was even 15' from the shoulders, you'c be talking about 750,000 foot pounds of torque, and trying to hold that with muscle tissue...
That's basically crazy. To my knowledge, there is no screw or bolt on anything in the world which requires more than a few thousand foot pounds of torque. The only thing in the world which would correspond to half a million foot pounds of torque or anything like that would be the combined max torque of all of the engines of the Yamato or the Musashi or some such.
Yes, I know... I was trying to get our friend to get to square one (pun) before going on. I believe I mentioned the moment arm on the neck which is what I was alluding to. I once calculated the forces on a dinosaurs neck for one of our other skeptics on another thread and you're absolutely correct. The materials of the neck made of bone (Hydroxyl apatite) and tendons simply could not do it. Bone has a tensile strength of about 52MPa (megaPascals) or about 7500 Pound per Square Inch. . . It wouldn't be too many cantilevered feet out before the leverage weight of a 50,000 pound neck on a single cervical vertebra would be greater than the bone structure could support at one G, to say nothing of the soft tissue between the vertebrae or the tendons and muscles to move the neck. Try holding your arm out with a five pound weight and see how long you can hold out.
When a bird's wing increases in size, the muscles and bones required to support it and particularly to FLAP the wings, have to be commensurately stronger, hence thicker and longer, changing the form factor of the bird. I.e. A deeper chest and wishbone. The cube-law. . . Greater weight means more wing to support that muscles, then more muscle. . . Means more wing. . . More muscle. . . And on and on until the wing cannot lift the bird. . . Diminishing returns unless there is a more efficient muscle. There isn't.