Maxperson
Morkus from Orkus
I don't have an issue with the class feature going against the intent of the spell. Why? Because D&D is at its heart an exception based game. It sets up rules and then immediately goes about creating exception after exception after exception after..... Every one of those exceptions goes against the intent of whatever it's the exception to. So while using the class feature goes against the intent of haste, it is right in line with what the heart game is all about.No. It is more proper to say that it is ambiguous, in the strictest definition of something having exactly two distinct and contradictory readings. Either the spell's limitation of what the special attack action can be used for takes precedence or the ability's expanding of what attack actions can do takes precedence. I see no determinitive reason to read one way or the other as more correct. I personally, like a number of people here, would interpret a spell as being the more specific thing then a subclass feature that the character can use every turn, and say specific beats general. But I can see how someone could reasonably call a subclass specific feature introduced at this point in the publication history as "more specific" than a frequently used spell available to a variety of character builds since the beginning of the edition. I don't agree, but to my knowledge there is no clear rule for when a spell should be considered "more specific" than a subclass feature.
I do feel that allowing the single haste action attack to become a cantrip goes against what seems to me to be the clear the spirit of the spells intent more than not letting a Bladesinger cram a second cantrip into their turn seems to go against the apparent intent of an ability that (at least to me it seemed) was introduced so that their getting the extra attack feature wouldn't be at odds with their use of cantrips anymore. But, that is a RAI argument, and one based on a lot of vague supposition, and maybe the skeleton of a best ruling argument. RAW-wise there is really no clear right answer.