Tell me more ? I'm curious as a Powerfully owner with none of the issues listed .
Its been bullet proof for the last 4000km and i do not go lightly - literally or figuratively !
Mine is a 2018 , previously to the rib design battery - rear wheel is getting a bit graunchy .
4000km with no issues. - A massive congratulations to you Sir !!
I am not familiar with the 2018 powerfly so I can't comment on that bike.
For the 2019-2020 Powerfly and Rail there are a number of common issues.
Specific to the Powerfly and Rail a number of owners have had the lower shock bolt snap. It's a hollow bolt made of lightweight aluminium. However I have known 110kg riders who have ridden DH bikes extremely aggressively without ever breaking a lower shock bolt, I've never even heard of it being an issue on other bikes.
The RIB battery is a total failure. Understand that this has been designed with input from bosch and abus. Now for normal city/road ebike use the design is adequate. However as soon as you start riding more aggressively it just doesn't hold up. I should also point out that trek released a "service bulletin" to all their bike shops on how to adjust/tighten the mounting bolts securing the battery because, get this, they were arriving loose straight from the factory !
If you completely strip the frame and check these mounting bolts you will never find loctite or any other thread locker. Even if you adjust the bolts and get everything tightened up correctly if you are riding hard, it's just a matter of time before things work loose. Now many people get around this by adding foam, tape, padding, etc.. to the battery however this can cause other issues. For example if you pad the battery it might stick out 0.5mm from the frame. This gap can then allow water, etc.. to get into the frame and run down to the battery. Not an issue in OZ, but totally screws the poor sods in the UK.
The knock block is another design flaw. I've seen multiple frames crack at the head tube (granted after a crash) where the force from the frame has travelled to the knock block and cracked the frame at the headset.
The paint of the new Rails is also very thin and many people report paint chips and damage after only light riding.
Another wonderful design flaw on the Rail is where the locking ring on the crank/motor comes loose because it unwinds in the same direction that the crank rotates. This can then cause the chain to jam which might get caught in the frame, foul the motor, break the chain (best case), ruin the chain ring, who knows. Although to be fair this is not specific to Trek, but rather an issue with the gen4 bosch motor.
So why haven't they fixed these design issues you might ask? Because they want to save $$. They want to keep using the same frame moulds from last year to save money. The 2020 Powerfly's were the same frame/mould as the 2019, just with new paint schemes. Same goes for the 2020 / 2021 Rails. Also having the same RIB system in all their city/commuter ebike and emtb's saves a fortune in economies of scale, saves on parts, etc.. Also for commuters, the RIB system is EXTREMELY easy and convenient.
To create a new battery mount system they would have to make sure that they don't infringe on another manufacturers design/patent. Then they need to work around the design of the Bosch batteries. Bosch is not going to make them a special battery.
Then of course there are other issues such as the freehub bodies being destroyed because the soft aluminium of the standard shimano XG freehub cannot deal with the torque of an ebike. But to be fair that's something I guess you could expect with all ebikes.
I would not buy a trek emtb or recommend one. However if you considered upgrading at some point the most important thing is to have a good ( & profitable) relationship with your bike shop and then sell the thing before the warranty runs out. If you have been buying Trek bikes from your LBS for 15 years I have no doubt that they will help you out. Maybe wait until the next frame design refresh which might address some of these issues.
In the mean time you can demo these ebikes for $150 for 3 days from any trek owned shop.
TLDR: Most people buying these ebikes are Dentists or older riders cruising on XC trails and there is no incentive to design them to suit long term enduro style riding. When buying an ebike the most important factor is warranty and whether your shop/brand will honour a warranty claim.