Absolutely no, if you're doing landscapes/architecture, heavy cropping, large prints.
Also, when you upgrade from 5DIV, 45mp sounds like a decent jump on par with Nikon D850 and Sony A7rIII. 39mp is a kinda meh.
Keep in mind with the R5 we should also get the new type of high detail low pass filter first found in the 1D X III. So even a lower megapixel bump could give you a greater than expected improvement with regards to detail.
Also worth noting is that Canon usually increments their resolution by a factor of about 1.3 between generations. And that would actually would mean 45 MP is the odd choice if the R5 is an R / 5D IV successor.
6D to 6D II => 20 * 1.3 = 26
5D III to 5D IV => 22 * 1.33 = 30
Older APS-C => 18 * 1.33 = 24
Newer APS-C => 24 * 1.33 = 32
R to R5 => 30 * 1.33 = 40 ?
Maybe they simply abandoned that approach for something more practical. 45 sounds nicer than 40, but it is no make or brake difference to me and probably not to the market either. As you can see above, it would be no unusual increment for Canon, and this time the speed and AF are getting unprecedented improvements to go along with it.