If you focus on leveling one single team to max, but leave all your other heroes as lowbies, you’re going to have trouble in both war and raids. If that one single team is 4*/5*, the problem becomes worse.
3* heroes are relatively easy to get and fast to level. They require no unfarmable ascension materials to fully ascend. And they have quite a decent array of effective powers.
A developing player should be able to get together 6 war teams of 3* relatively rapidly (order of a few months). And from this base, start adding 4* heroes where they are most useful. If you do this, war looks little different from rading in terms of ease of fights.