If you’re talking about war, then that’s clearly not a team you should be taking on if all you have to field are 4* heroes. If you’re talking about raiding, this might be a hard pill to swallow (and I was there too, believe me), but you’re not REQUIRED to fight every raid team that comes up. Some teams are better to just walk away from.
In general, I’d say that as emblems become more prevalent and people put their strongest defenders up in teams that yes, blank 4* max heroes are of increasingly questionable value, an observation that Zephyr mentions in this post: Clicky clicky
It’s possible to take out 5*+20 heroes with vanilla 4*, but it’s like taking on a vanilla 5* team with 3* heroes. You need to go full mono and hope the tile gods favored you because the statistics gods make that a swing-for-the-fences scenario. I forget who said it, but it was in a thread similar to this one, but once heroes get to 5*+20, you can take them out with blank 5* max heroes and 4*+20, but it’s like from the old days of taking on 5* defenses with a 4* team, all before emblems existed; you need to stack heavily and hope for good tiles. Vanilla 4* are now like 3* in that scenario, so not that great at all but without emblems to give them some extra oomph, yes, they’re kinda questionable.
It does create this interesting effect of devaluing 3* ascension items because, heck, why should I waste my shields on a vanilla Peters if I don’t have the Rogue tokens to give him? Not a great place to be in, I agree.