Those must have been some quite shallow ISTPs then. It's very easy to classify ISTPs as INTPs without imagination based on all of the descriptions that get thrown around everywhere, but I'd say that that's far away from the truth. It's not that ISTPs lack the imagination, nothing like that. The "amount" of imagination is not a factor in this case, the "kind" is. ISTPs are stereotypically more practical in nature, while INTPs are more theoretical. You could argue that imagination is theoretical in and of itself, but I feel it would be a pretty weak argument.Stereotypical ISTPs= real life ISTJs
Stereotypical INFJs= real life INFPs
Most of the ISTPs I've met in real life are just like INTPs without the imagination, honestly.