Imperative tends to be the simplest verb form, cf. Latin dic, fac. English is not very inflecting, so other verb forms can be just as simple as the imperative. Nevertheless, is there a language, where another verb form, e. g. 3 sg present or past, is more basic (more similar/closer to the bare root) than the imperative?
Classical Arabic may provide an example: see section 6.1.3 of Brame 1970. His account is that the affirmative imperative is formed by truncating the subject prefix ta- from the 2nd person jussive, and then other rules may apply as appropriate (notably, epenthesis of a harmonizing vowel if the stem has an initial cluster, so /ta-ktub/ → ktub → [ʔuktub] "write!", but /ta-wṣil/ → ta-ṣil → [ṣil]). The imperative would then be a bit more complex than the jussive, in that it is the jussive plus a few added steps. Similar analyses could be given to Norwegian imperatives, which may derive by a truncation of the infinitive suffix (if any), subject to complications when the result would end in an impossible cluster. All such cases that I know of involve deriving the imperative from something else, by chopping off an affix from that other form.
For the German language there is a form called Erikativ or Inflektiv which is just the isolated verb stem. It is arguably simpler than the imperative singular because for some strong verbs there is a vowel change in the imperative singular (e.g., treten, tritt, stem tret "to kick"; geben, gib, stem geb "to give").
The Erikativ is predominantly used in Comics, but it has also entered computer mediated communication (like chats or blogs).
Note that, in Latin, the normal imperative is e.g. mitte, where the first person singular is mitto. So at least for some verbs the first person singular is as simple as the imperative. But, generally, yes, imperatives are among the simplest forms.
In Greek, it depends on the verb. For most verbs, the imperative is short. But there are verbs where the imperative is considerably less simple than the past third person singular, notably in the aorist, where the latter can be the bare root/stem:
ΓΝΩ : "he knows / knew / has come to know" (aorist third person singular indicative without augment)
ΓΝΩΘΙ : "know!", "you must know" (aorist second person singular imperative)
It is possible that this imperative ending -ΘΙ found favour at some time because it made it easier to distinguish those two forms. But I don't know: perhaps this -ΘΙ is in fact a very old imperative ending that was in continuous use from Proto-Greek or Proto-Indo-European. This might be a good question to ask on https://latin.stackexchange.com/, where Ancient Greek is also on topic.