I'm not trying to be snarky here, but, if you aren't enjoying spending 10 hours a week on a hobby...why are you doing it?It's obviously not fun for you to "convert monsters, develop encounters, plot storylines and brainstorm", so why do it?
Before running any plot-based adventure, it's important to get buy-in from the players that they will endeavor to stick to the plot and will come up with solid justification as to why their characters care to see it to the end. What you don't want to do is tell them it's a sandbox game and all roads lead to the storyline. That's railroading. But if you're upfront with the players and get their buy-in, then concerns about railroading go away because they have agreed to stick to the plot. If that's not your bag, don't run or play in plot-driven adventures.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.