To make them cover their own lacking traits, you would like an All-Skill Access relic. As long as you have ways of keeping them alive, All Skill Access and halved cooldown are viable options.
For example, when you hired Scoundrel you always pick Night’s Veil, but right across Vanish provides cheat death and covers you for up to 7 seconds, the longest duration. When you tag along with Templar, you bring him over for his Heal and Charge but right across he has Intervene and Onslaught for crowd control. While you have Enchantress, you have to pick between her Amplification and Prophetic Harmony, or miss out Fate’s Lapse for the sake of Focused Mind.
Only pet oriented builds equip Enforcer and as a result, usually pet oriented builds prefer other non-Invulnerable tokens on Followers. However, you can still get them protective powers and ignore Enforcer but you really need to play around your Follower in that case. Either you stick to their side by watching them from mini-map constantly, or consider high mobility so you can push and get them teleport to you from further than 75 yards.
In example; Burning Axe of Sankis, Rogar’s Huge Stone, and St. Archew’s Gage (non-Season don’t have Altar, you know?), all work for Followers. In any case, there are also items such as Genzaniku or Maximus to summon creatures forth to get some burden off from them and they’ll keep fighting after Followers take a break.
It is not a bad thing that Followers knelt down in combat; they will resurrect in 20 seconds but you’ll have all the missed monster aggression on yourself. This only would force you to kite monsters a while then prioritize the meanest targets. Just don’t click any revealed Pylon when Followers are down, and use this opportunity to pull monsters around the Pylon.
Some builds with high sustain or high defense, wide reach but lacking range prefers Scoundrel to boost damage with Night’s Veil, but him lacking any protection on the character cause players to ignore him. Yet, he has the best cheat death ability amongst all three.
Also on theory, you can give Scoundrel a halved cooldown token and watch him lay Night’s Veil every 15 seconds which would match the cycle of most CoE oriented builds. No idea which build can utilize him that way, but it’s an option. You can easily give him a Broken Promises (Followers have 0% Critical hit Chance as base) and Pus Spitter to trigger it, to benefit almost constant Hysteria ability buffs.