The question is not if the models have been reused, but if the reused models are outdated. Could they have higher polygon counts and neater corners/edges with 10 more years of graphics development? Sure. But it does not always make sense to improve the complexity of your models, especially if you're not going to see it once you're zoomed out. At this point you'll just increase power consumption on the hardware for no benefit. On zoom-in, you'll probably see some of the rougher edges, but there is good reason for the developer to prioritize performance over that last 10% visual fidelity. You personally might weight that differently and not recommend the game with good reason as well, but that's not the only way.
I would have also expected an overall larger graphics leap, but I don't find the graphics particularly bad. For me it was more the overall art design that was slightly off and did not yield this great immersion that CoH2 had, but this has to do with more than just graphics. I have to say that I did not play the release version and that the data that Relic has put out since then looked promising on the graphics side at least.
I find it quite annoying though that many just jump on one single issue and downvote the game because of that. I don't believe that the e.g. graphic issues are so large that THAT many people find it game breaking. The game is more than just graphics or a couple of models ported from CoH2. They just expected better or something different and downvote in pure defiance.
Here my annoyances are well explained, they are not only low poly models, but the textures and shapes are not well sculpted and there are even invented parts, you can only get a single tiger in the game I don't think there were performance problems this is simply neglect, what is not normal is that the remodeled backpacks for coh3 that are seen on top of the tank have better modeling than the tank itself hahaha.
I assure you that a much better modeled model would not decrease performance at all.
https://imgur.com/a/fsSj92A#6NXM3wY