If it sounds right, it is right. I always thought of it as a sort of in-built tubescreamer effect on the 81 - like an additional gain stage. Can give you really cool, compressed sounds.
Humorously enough the 81-7 I put into my Hellraiser sounds like SHIT compared to the 707, so you never know. The woods and construction may interact more than we realize. The 81-7 made the all-mahogany/rosewood hellraiser sound like it was all maple and alder *shudders*.