if you're not altering code or manipulating the game through some non-Blizzard approved means or interface in order to produce an end result where you are the first to turn in the quest on sunday and be awarded the prize, then it can't, as a rule, be the "wrong" way... or ever the "bad" way...
it's about the moment... it's not about the Extravaganza. by "about" i mean, in-game fishing, and thus, in-game relations amongst anglers and ultimately all other players... they're sort of comparable to the Great Sea in which the Stranglethorn Fishing Extravaganza is, at best, a rare fish... and by no means the rarest.
the achievement to be found through in-game fishing for me is 'about' patience and simplicity, and the variety to be experienced through such a very simple formula: angler on shore + fish in the water / the bit of string that's (hopefully) connecting us. ... the only influence i intend for my fundamental process to have on fellow anglers is that if i happen upon one of you patiently fishing a school, i /greet and carry on. THAT'S the prize, really. existing in a world, albeit a virtual one, where i only allow my influence to be positive (positive, in that, hopefully, i leave no one feeling that their time on earth would have been more enjoyable had i not been even the briefest part of it), and ideally where i have no perceptible influence on another individual if none is warranted or wanted... especially if it would hamper the enjoyment of something as simple as... video game fishing.
basically, "mammoth blocking"/Personal Rival Angler Hit Squads... sure, those things are legal. and they definitely work. and if your only goal is to acquire yet achievement, they becomes logical precautionary measures.. they might very well be the only way to gain that edge over better studied, more experienced anglers.... they're also disappointingly easy.... and indicative of that fundamental weakness of character inherent in all 'must-have-at-all-cost' types. you know who you are... because you're not here, reading this... you're out there NOT smiling and saying "oh, pardon me" when you and another person bump into each other or parking directly in front of the store entrance in the area clearly marked "no parking - fire zone" but turning on your hazard lights as if to say "oh, no... i'm only temporarily parking here because i just needed to do some shopping here." or using the "10 items or less lane" when it's obvious you've got no less that 30... or organizing your time and energy around the sabotage of your betters... those persistent and self-contained few for whom their own values and integrity mark the narrow path by which a goal must be achieved if it's to feel at all valid or rewarding... all so that you don't have to worry about ever being good at anything other than undermining those who ARE good at something.
...even if it's video game fishing.
so i have the utmost esteem for those dignified souls that COULD so easily and even justly hinder my meager efforts as a means of furthering their own gains, but still don't... and will not. which is essentially, everyone who doesn't do it... and who opts, instead for a more cooperative atmosphere for a competitive event.
to the OP, don't think your method of winning is one i find abhorant. It's that i wish it would've been one i couldn't help finding admirable.