For the sake of explanation, let’s first look at a set of sentences in which 舐めた／舐めていた／舐めている modifies a concrete noun.
The tense of the main clause is the present as in your example. Despite the similar difference in tense in the part before 飴, you should have little difficulty distinguishing their meanings. The action of 舐める happened at a specific point in time in the first, whereas it is a past and current habit in the second and the third, respectively.
Now, let’s look at another set with a more abstract noun.
Here the verb 舐める is used figuratively and the 〜ている form in this usage is more naturally understood as describing a state in mind than an ongoing action or a habit. Otherwise, there is not much difference from the first set. The act of underestimating the opponents happened at some specific point in time in the first (perhaps at a planning stage before the battle began), whereas it is a past state (perhaps when the battle was still at its early stages) and a current state of the speaker’s mind in the second and third, respectively.
This doesn’t fundamentally change in the following.
What is not your “intention” (つもり) in each corresponds to what is denied by 〜訳ではない in the set above.
With regard to the additional question (in the comments) about whether
把握していたつもり can be replaced with
把握しているつもり in the following example, my short answer would be “yes.”
I guess what is happening here is like this. Technically speaking, the
把握していたつもりだった is supposed to refer to a state at an earlier time than the time at which she thought it was her “intention” (つもり). However, with no expression in the sentence that clarifies when it was, this time frame gets shifted forward and merged into the latter time and thus blurs the distinction from
把握していた could be understood as describing a completed state. The punctual act of 把握する had happened earlier and she was already in the resulting state of 把握している at that time, or that’s what she thought was the case.
把握していたつもりだった works better than
把握しているつもりだった in this case, although the final state (of “understanding”) she thought she was in is the same.
Here is my attempt to explain the difference with English translations.
I thought I understood it (then).
I thought I understood it (then). [same as above]
I thought I had understood it (by then). [completed state]
In the first of the two English translations, the verb “understand” is used in its stative sense, to describe a past state in mind, whereas in the second (last), the same verb is used in its punctual sense (“grasp”), to describe a change of state that had happened earlier. The result is the same. She thought she understood it in the end.