Three comments:
Firstly the Englineer unlock requirements will encourage a player to engage and gain a basic proficiency in aspects of the game that they may not previously have tried. I think of it as a sort of in-game training, or at least a framework for self-study. Sure you may not 'click' with some game roles, but similarly, somewhere aong the enginner unlocks path, you might be put in contact with something that you like.
Secondly (and I say this for long term engagement in the game) The game is a mile wide and an inch deep for those who accelerate progress/wealth gathering. If you skim a stone across the surface or the lake of ED, your stone will end up on the other side, and you'll think "What now??" (having totally missed the content and varied gameplay in the depths of the lake). Alternatively (or possibly in addition), you'll be at what is intended to be an advanced position in game, without the experience/knowledge to play effectively at that level.
For sure some of the game loops will not be a particular players cup of tea, but doing it just the once will teach that player more about the game. For example, My two main commanders play as "Lawful/good". I really hated having to unlock The Dweller (deal in 5 black markets), and had to work hard to find the least out of character methods to comply (as it's only a game, and the prize is behind an artificial gate, as well as there being a game mechanic to learn).