There is a corporate climate answer here, so you have to handle this within your own corporate climate.

A very important thing in a producer/consumer relationship is to be able to manage expectations. Consider this situation:

Customer asks for A, you do A immediately. Customer is happy

Customer asks for B, and you do B immediately. Customer is happy

Customer asks for C. C is harder, so it takes you time. Customer understands that C is difficult, so they accept it.

Customer asks for A again. You can't do A immediately because you're busy doing C. Customer asks "Why can't you do A quickly? You did it quickly before."

The next step in that story is very context dependent based on your relationship with the customer. You have to be able to explain to the customer why A can't be done as fast as it was done before. That might involve introducing them to exactly how hard some of these tasks are to do. Or it might involve them accepting that you are a go-getter that opportunistically did A when it was easy, and now needs to schedule it.

Or they can be the kind of customer that's furious that your production schedule no longer matches their expectations, and you can lose their business.

Or there could be a complicated system (like billable hours) which you didn't know about and are accidentally causing problems with.

Your boss is the one responsible for this. Work with them. Make sure they understand that the consequence of your pro-active approach is that it won't always be there. Make sure they understand that when they fully task you with all sorts of stuff, you won't be able to just interject those quick turnarounds.

In some environments, the boss will say "great. Keep doing the fast paced work. I'll cover for you when you hit 100% load." In other environments, the boss will say "Let's focus on managing expectations, and ensure the customer not only is happy, but stays happy for the long haul." Answering those questions is your bosses job, and you job is merely to provide them the resources they need to answer that question.

If your boss is happy with your approach, then that's what matters.

All customers like to be satisfied in the short term. All customers like their producers to be able to offer fast turnarounds. Some customers understand the long term implications of these fast turnarounds, while other customers would prefer you and your team to manage them.

And in this case, the big difference between your boss and your customer is that your customer may choose to be interested in the long term interests of your company, or they may choose to do their own thing. Your boss should always be thinking of the long term interests of your company, and can provide you such guidance.