I for one definitely do ahve a rational reasoning.
The game currently is starved for content and it’s a live-service game.
To keep a live-service game running you need to keep people long-term in it if possible, unless you have a very massive amount of people coming and going regularly… but in a steady way. And even then it’s extremely risky to not have the long-term engagement happening as it can dip over at any moment.
While mastery unlock doesn’t directly reduce the overall needed time to reach the end-line substantially the majority of players are shorter-term players which invest 20-40 hours into a character. The shift allows them to bypass roughly 5 hours (which will be what is commonly needed for a second playthrough by many people) of those. And that’s a substantial amount of time for what they will experience rather then what the game has in total to offer potentially.
And more importantly, it reduces the mental barrier to allow switching to another character and hence re-doing the content comparatively to pushing on and reaching a higher goal.
This causes problems in several avenues.
One, a significant amount of people are not mentally proclined to re-do things, for them it’s a ‘one and done’ thing. Doing a second character substantially leads to mental fatigue for some of those, which can cause a earlier stopping of the engagement with the game - bad enough - and even worse sustaining that fatigue over to the next Cycle and potentially skipping that.
The second is that it actively reduces the long-term value of the game in the current state. Build variety is for some odd reason regularly praised while it’s the lowest (without counting D3 and D4 which are near pure ‘tourist’ games) in the whole genre, including single-player games of the same setup-direction. You simply ‘have seen it all’ and EHG is not really quick with their meta-shifts. You run in danger to simply have nothing interesting to play anymore which actually is enticing for you.
The third is that limitation of choice provides a psychological weight to said choice. It’s a general thing with limitations, much like the experience of gathering materials in a survival game like Minecraft and building a nice great looking home there is far less valuable when you clobber it together in creative mode. Effort and struggle - if provided at a reasonable amount - does enhance the experience for the end-result.
Mind you… with more content variety it’s a absolutely feasable and even reasonable thing to do.
It’s just that EHG did it prematurely, they’re absolute masters in ‘doing the right things at the wrong times’.
Sadly they also sprinkle it with a bit of ‘doing the right things the wrong way’ on top of that 
Projecting is neither positive nor negative, it’s simply a behaviour. It’s more worrying that you imply it being purely negative.
Also yes… it is projecting since it’s not based on factual information but subjective experience. This causes to ‘project those experiences’ into the reaction.
That literally is what ‘projecting’ is.
Projecting can enhance your personal experience, ‘wearing rose-tinted glasses’ is a prime saying after all which directly relates to that. The negative is removed and the positive is the only thing experienced for the person, which is a subjective state as the reality is a different case. But for a entertainment product this is a net-positive thing to happen for the customer.
Especially in an ARPG.
Look at what happens in ‘Dwarven Realms’, you switch between builds without any form of downside. This makes every single way to play feel ‘generic’ as the contemplation of limitations, hence upsides versus downsides falls away. It’s solely about the most efficient way and not ‘making something you’ve already invested in work’.
That’s a substantial amount of the enjoyment players derive from this genre.
The important part from the devs hence is to ensure balance is not too outrageous, hence stays within a limit to not cause non-optimal choices to feel utterly awful and optimal choices to feel mandatory.
That’s one of the biggest aspects LE struggles with anyway, which makes it seem viable to use the workaround since it improves the experience by avoiding those pitfalls.
The reality is those pitfalls shouldn’t exist and the limitations hence enhancing your experience rather then being a detriment.