I believe the idea was to allow tanks to be able to push turrets if they wanted to "build" into it. They did this with AP users way back by adding AP ratios to their autos on towers. It actually ends up taking some power away from ADCs, in the AP case it made it so ADCs dont have to be the center of all team fights because now others can take towers. With Demolish now, its the same thing, now other champions can push towers instead of ADC, so ADC doesn't need to be protected like some god that can never be allowed to take a single hit; it also takes away some power early game from them because now its conceivable for a tank to get first turret outside of cases where you somehow kill the enemy top laner 3 times in 8 minutes, which is something tanks needed to compete a bit better early game, as well as attract people to the role.
Now, since it's on a rune they had to up the power to allow it to give the same impact to tanks, and against ADC centricism as those AP tower-pushing systemic changes gave AP users. This may be causing a problem of putting it in a precarious position between giving the amount of impact it needs for tanks to solve their particular issue, vs. feeling really bad to fight against. Some of the feels bad will go away with time, but it may be too much even after that settles.
Red buff was probably an anti-turtle mechanic, and since those days it was needed for such, it has become very centric to objectives available. What I mean is, people like the impact it gives, its very meaningful. It's power has been reduced over the years I would like to point out, and currently it's power is spread between a bit of extra tower push(it's honestly not much unless you have a lot of AS) and PvP damage, so it isn't as centric to pushing towers as you might think. Also there's counter-play in that you can kill the person to not only to make them lose it, but you get it. Anyways, the buff is too popular to be touched and is actually really balanced right now anyway.
Also these changes are actually a pretty big buff to towers, its +5% damage reduction at the start essentially. All in all the changes probably mean towers stay up a good 6-7% longer during laning phase, which means laning phase lasts longer.
The triumph changes are just because it's OP, by far best in slot. And that extra gold is also most impactful early game, so since laning phase has gotten shorter recently they overlapped its nerf to help that as well.
As for your proposed changes, how does lowering the health scaling affect it's early game damage, which is what you're complaining of?
that has a redemption sized range activated, that drops a scaling shield, or increases the turrets fire rate and gives it aoe or something
