Thanks for the feedback and playing the game! I understand what you mean about the non-puzzle elements. My aim was to create as many interesting levels as possible without recycling too many puzzle ideas from other levels, so I thought adding the sentries would give me more material to design with overall. Making them easier may have been a remedy to the problem but I felt like it wouldn't have been a challenge if that were the case.
When it came to those time challenges and levels that you need to lose before realising what you have to do, I think I straight up made the mistake of thinking annoying the player in that kind of way was good game design.