My experience with Vudu is that the maximum bitrate is high enough if you have sufficient bandwidth to take full advantage of it that visible artifacts are rare on MOST content. There can be a lack of black level detail with some material in HD, but that goes away entirely with 4K HDR material. If I were to lay it out in percentages, I would say Vudu gets you about 90% there with HD material compared with disc.
If it is not quite as good, why did I got that route? Cost. Being able to get an HD copy of a movie I already owned on DVD for $2.50 was hard to say no to. That was also around the time the secondary market for Ultraviolet movie codes popped up. I was able to buy new release movies in HD for $6-8, which was also hard to say no to. That allowed me to buy a LOT of movies at affordable prices. I would estimate that 1000 titles in my library are either disc-to-digital or after market redemption codes. I stopped doing codes because some of the studios changed their terms of service and I did not want to risk losing my account. The fact that 4K codes were only marginally cheaper anyway made that decision very easy.