I don't see what's so great about ablative armor, when by definition it's armor that works by partially disintegrating/vaporizing when it's used, absorbing the energy of the impact by taking damage itself rather than propagating the damage to the vessel within. So it would have to be replaced after every battle, like the Space Shuttle's heat tiles had to be replaced after every flight. It seems very inefficient and cumbersome compared to energy shields that you can just turn on and off.
Energy Shields are the "Primary" form of defense, but as in many battles, we have seen that "Shields" can be brought down either temporarily or permanently (for the duration of the battle). Or out-right bypassed if you can somehow steal the Frequency Modulation of the Shields as in ST:Generations (The Duras Sisters planted Malware in Geordi's Visor which leaked Visual Information to the Duras Sisters).
The point of Ablative Armor is similar to
Chobham Armor IRL, it's a quick to replace system that absorbs alot of hits from Energy Weapons and slowly wears away, leaving the core Hull/Structure intact.
So that once you return to the StarBase, it's fairly easy to remount new Ablative Armor panels and send your vessel back out as fast as possible.
Core Hull / Structural damage on Ships or Tanks can take a vessel out of commission for weeks / months / years depending on the damage and how fast you can repair something based on available repair crew resources and available parts & supplies.
A modular replaceable armor that can take several hits allows for quick & easy logistical replacement.
There's a reason why modern Ceramic Body Armor panels for people to wear is designed to be quick and easily replaced.
People going down, they can either be permanently incapacitated, temporarily, etc.
Body Armor panels are cheap and easy to replace, well worth the cost compared to the lifes of the person it protects.
Without Shields, you can potentially be One-Shot by just about anything once Shields are down, it's always a good idea to have "BackUp" solutions for defense once your "Main Shields" are down. And Energy Weapons are the most common form of offense next to a Torpedo/Missile of some sort. But Torpedos/Missiles are far easier to dodge/intercept with weapons fire, then Energy beams that travel at the speed of light.
You know how in the ST:VOY episode where Janeway had to face Ransom and the Nova-Class StarShip Equinox had one very cool / unique feature. The ability to quickly recharge the Shield Capacity to Full if taken offline for 45 seconds. That feature is similar to how SmartPhones are easier and quicker to recharge if the device is Off and you have the Best Quick Charge Wall Wart available to feed power into the battery.
Now imagine the future evolution of that technology where you have 2x / 3x sets of Emitters and Shield Systems that are largely independent of each other that can create "Ovaloid Shaped Bubble Shields". If one set goes down or is turned off when near empty, the computer can turn on the other set of Shields quickly in a split second and have rotating sets of Shields to defend your vessel. That makes killing your vessel that much harder since they have to "Alpha Strike" your Shields through "Multiple" Sets of Shields and hope they have enough Sustained FirePower to punch through a "Full Capacity" set of Shields each time.
Hypothetically that makes the enemy need to punch through 100% of your Shields in < 45 seconds and sustain that FirePower for the second set of 100% Shields while your other set is quickly recharging. That could be "Tough" depending on how good your default Shields are.
Add in Multiple Layers of Shields like say a "Skin Tight" shield that conforms to the surface of the hull, we've seen that before many times. I can see a future with "Multiple Stacked Layers" of Active Shields before you even factor any physical Armor onto the hull of a vessel.
Then you have to figure in Ablative Hull Armor Generator that Janeway brought back that can be replicated on top of the default Hull. The default Hull would of course already have Ablative Armor panels that are installed on top of the base Hull.
This gives you a nice "Tough Vessel" that makes it "Hard to kill". Many layers of defense for the opponent to get through in short order just to destroy you.
That's how I see technology progressing for Defense in the future of Star Trek Technology past the 24th century with all the evidence Defensive Technology/Capabilities I've seen in cannon ST works alone.