Part of playing a good DPS is to learn how to focus fire, but most people don't do it. Heals are not OP, just that DPS need to learn to play better.
That's just not the case, if you're killing healers, it's often because THEY are playing badly or not evasively enough, especially Scoundrel/Operative whose probe/medpac FAR outdoes mobile damage of all ranged specs and many melee specs. If all you're doing is chasing a healer who is constantly running, LOSing, etc, then you aren't doing damage or taking objectives, which means you aren't achieving anything productive.
The worst part is, it isn't even optional. If you chase them, you're not achieving anything. If you DON'T chase them, they freecast. It's a literal lose-lose situation that becomes worse the more players are involved.
A sniper or marauder can theoretically stack enough cooldowns and burst abilities to take one down, but that's a completely inane way to justify healing as "balanced". "Well 2 of the 18 dps specs in the game could theoretically burst down a healer with no cooldowns of their own who sits there and takes it, so healing is balanced." Completely insane.
Stacked healers makes things more difficult. Have 2-3 people chasing 1 healer, and said healer is themself being healed extensively by the other un-focused healers.
Warzone results consistently show healers above dps, often by very large margins. What people overlook is that dps values are INFLATED by a lot of wasted cleaves, AOEs, DOTs, that never endanger someone and don't kill anyone and are easily meditated off. It's VERY easy to spam Corrosive Grenades and Shrap Bombs to inflate damage numbers while achieving nothing whatsoever.
Healing, however, is UNDERstated in the results, where overhealing and unused absorbs aren't included. This actually means that the true output of healers is even HIGHER than results typically reflect. So not only is it mathematically FAR easier to achieve high healing numbers, those numbers are actually understated, whereas a lot of damage numbers are inflated and overstated. The margin between healing and dps is considerably higher than scorescreens will ever reflect. If you see 1 million healing to 500k damage, the true discrepancy is more like 1.2 million to 400k, or even wider.
This is a simple observerable mathematical fact.