The Spinosaurus is clearly bigger than the Rex. While in JWE the difference is barely noticeable even if you are looking for it. Yes, it should be even bigger than what it already is (compared to the Rex). But it took an incredible amount of effort to make them change sizes one time. They won't do it again. No point in keep bringing it up.
The JP3/TLW Rex is still smaller than the Rex we have in JWE, because the female Rex's are bigger than the males. We've never seen a Spino against a grown female T-Rex. Only a young adult male.

Bull the T-Rex (Jurassic Park III)
Bull or Freddie is a young adult male Tyrannosaurus Rex and was a minor antagonist in Jurassic Park III. According to the official size charts, he was 11.2776 meters (37 feet) long and 4.4196 meters (14.5 feet) tall, a little less than others T. rexes in the Jurassic Park series. as the...
So of course it shouldn't be the same size difference as in JP3.