Let's not be too hard on SE about BLU and in general.

[Alleo]

Well when I read up on Blue mage they seemingly have in common that they get their skills through the monsters they fight but even there how they get it from them is quite different from each game. So Blue mage in FF14 who would learn certain basics skills for duty content by taking on quests to kill certain monsters and get certain skills from them would still be like other blue mages just with a quest marker as the guide line. (And seemingly it was not all the time OP either.)

The death skill could also still be in the game but simply either locked for duties or just dont have any effects on them (or less effect on monsters in duties).

So even with some balance the basic of the job which is getting skills from monsters would still be there. You are also even with that limited job limited. Its not like you can go around and get every single monster spell in the game. You might have the ability to copy stuff from monsters but can only have 49 skills at release and can also use 20 of them actively. Thus you are already not 100% a blue mage either because it has restrictions. So why would it be bad if we got one more restriction in form of a certain rotation in duties? Again this would be taken away for solo content and the blue duty. There they could be as overpowered as they want to be.

So that way: New content, still playable in every other relevant content, overpowered in solo play, still has the identity of the job by getting all skills from killing monsters (just some have also quests before that).

They didn't say anything about how BLU will be treated in the future. The level 50 cap is not there by accident, it's because it's the level cap for the base game. If they only wanted BLU not breaking current content, it would be released with lvl 60 cap. And since SB came with HW, we can assume that SH will come with both SB and HW, so if you go beyond lvl50, then you can go up to 80 for the same price. And, again, SH content can de designed with BLU in mind, to limit how much the job will be broken.

They have made quite sure to say that this was a solo job and that you can only do the old duties if you use a premade group because it would otherwise be too strong. How exactly would it make sense for it to reach lvl80 in Shadowbringers? Because if that would be the case it could simply destroy any raiding scene because those endgame raids can be done with premades thus would be content that blue mage can do.

Also why would they design content for the new expansion with blue mage in mind if they stated that its a limited job and solo play. And they have said that one of the reasons they chose to go that way, was the fear that blue mages would be kicked out of duties because they would not have certain abilities. What change other than creating restrictions would change that? And if they use restrictions to make it playable in shadowbringer instanced content then why restrict it at all? Why not release it at lvl 60 and raise it to 70 at the expansion release? Why state that over the 5.x patches they will increase the levels but never said that its going to be max level if that would be that case?