Well, if the Matildas were meant only to engage enemy armor in support of infantry operations, then wouldn't that classify them as tank destroyers rather than tanks?

I disagree on this point. It was useful in an Alamein-style straightforward bashing operation, where massive superiority of numbers enabled the British to disregard any worries about enemy flanking counterattacks. But the Matilda was just too darned slow for any kind of highly mobile battle, which was the single greatest factor in the failure of Battleaxe under Wavell. His Matildas were just too slow to respond when the much faster German panzers counterattacked around the British left flank and threatened their supply lines. Wavell knew it would be foolish to split his forces by trying to split off his faster tanks from the lumbering Matildas because they would then be outnumbered by the focused thrust of the DAKs armor and that would have enabled the Germans to defeat his forces piecemeal. So he was forced to withdraw the entire attack force, and then got sacked for doing the right thing because his superiors did not understand why the attack failed. (Even though Wavell had warned them beforehand that the Matildas were just too slow for battle in the desert against the much faster German panzers.)