Guild Wars has enough restrictions if you want to maximize the amount of points you earn. The only thing removing scouting would accomplish is requiring the attacker to attempt everything using the most broadly effective team, which in turn severely limits your options for what you would actually use.
There is no extra "difficulty" if you can't scout. Having occasionally unwinnable matches because you guessed wrong with troop selection doesn't make the match itself more difficult. There are simply far too many gimmick instakill type troops to cover all bases with a team of a single color that is still fast enough to not be completely rolled by just brute force and versalitle enough not to run into the occasional gimmick that will beat you because you also had a bad starting board. This, in turn, largely diminishes the necessity to actually use a variety of teams, or tweak your teams depending on the situation.
When you lose, specifically in a mode like guild wars where it is set up for every win and the degree of how much you won to count, it needs to be able to be traced back to an informed decision. Either through choosing the wrong troops when you know what you are facing, risking using all of a single color knowing a bad starting board can screw you, choosing the wrong gem to swipe or the wrong ability to cast to give your enemy a drop, even sky drops giving a 4/5 match ligament spawned from your primary move, are all calculated risk assessments you can make. Not scouting and not seeing that deathknight, or that maw/mercy, or that valk/justice/mab, or that forest guardian/kerberos, or that bombot team, or that bone dragon courage, or that stacked famines, (etc etc etc) or just not caring and then getting the subsequent "bad luck" that causes you to lose would be on you. Not being able to scout period turns guild wars into a round of "guess the gimmick" to the point where I highly doubt anyone would willingly use mono color team and always bring their swiss army knife which would largely invalidate pretty much the most unique thing guild wars had to it, active counter-team building with heavy restrictions if you want to still win and be able to maximize your points.
Unfortunately, I'm still predicting the defense meta will be mana-drain heavy, which will also run this entire concept straight into the ground by leaving very few viable options for any given color.