I am 65. I have bred fish since I was 12. I have been building ponds for the last 30 years. I only build with steel reinforced concrete. The concrete is hand packed and cut. Expected lifespan 20+years.
I ONLY use products that have proven themselves over these years.
The sealant I use has been on the market for over 30 years. I use a rapid setting, plugging mortar to repair cracks and to seal around pvc pipes. This product has also been around for many years and has had 2 name changes.
Over time I have proven to myself that a SIMPLE High Pressure Biological System is adequate. It is simple and quick to maintain.
The pond has 1 or more 110mm bottom drains connected to a flush box.
The bottom drains are situated in 'dishes' at the deepest point of the pond.
An underwater return is included to move the water in the direction of the bottom drains. A weir is installed to remove floating debris...before it settles to the bottom. The System is driven with an 'open impeller' pond pump. (Earthco) A KOI Sand filter (NOT a pool filter)(I hear the detractors...if you do the correct maintenance procedures, it works fine)  and then to a Bio Booster (with filter medium) and an Ultra Violet Clarifier. Aeration is provided with a waterfall or water feature.
The configuration and flow volumes of the System must be controlled with valves in order to achieve Maximum effectiveness.
Rapid cleaning techniques can be achieved after a windstorm or the pond flushed with the use of the valves.
I guarantee Clean, Clear AND Healthy water ALL year round with this sytem.
It takes 5 mins. once per week and 10 mins. once per month to keep your pond in pristine condition.
I know there are ponders who delight in getting mucky, cleaning filters and getting down and dirty for their ponds. I have seen gardeners who prefer to use their hands rather than trowels...then spend time brushing the dirt from their nails...Bless them.
Then there are the Techno Freaks.
The trend is for huge Bio Systems that almost dwarf the pond in litreage.
Then the Fiddlers. I have seen rows of vortexes, bubbling kaldness, protein skimmers, rows of chambers with different filter media, etc.,etc.
All of this gunk is not at all necessary.
I know some people are in the business of selling equipment. Bless them too.
In answer to a challenge I took a sample of my water and a sample of a techno friend's water...(Bubble bead filter, vortexes, protein skimmer, etc.)
No real difference at all.
My aim has been to provide a long lasting pond and a great system to keep it healthy and clean with the MINIMUM of HASSLE!!! AND that is exactly what I can provide.

Couldn't agree with you more....... Each to their own tho!

All systems work, it's up to how much time and effort you are prepared to put into it!

You said it.
It's about how much time you want to spend MAINTAINING your pond.
My aim is to spend as little time as possible maintaining my ponds and spend MORE time ENJOYING my pond, feeding my fish, watching my fish swim about ...until it becomes a meditation.
Nothing religious...just being able to relax and chill out...take my mind off things...shut down the internal chatter.
That's MY take on a Koi pond. It's MAIN purpose, for me, is to provide a means to relax and enjoy.
I reckon I am a Koi Ponder...because I want to spend the maximum amount of my time with my fish...not tending to pond maintenance.
but as I said...You do get the Tinkering Ponder who must tinker constantly with his system.
The Techno Ponder who thinks BIG and expensive and complicated is the only way to get good water quality.
The Muck Ponder who is not happy until he is as smelly as all the layers of sponges and matting that he is constantly cleaning.
Ponders are all slightly insane. Most of us started off with a bowl or a fish tank and ended up with ponds that grow increasingly larger.