Okay, how about an average to above-average defender? Keeping guys from getting a step on you from the 3pt line isn't a size issue, it's a footwork/lateral quickness/effort/strength issue. If Marcus Smart was our starting SG, nobody would worry about the defense. He's no taller than Ant. It's too easy to chalk everything up to whatever the listed height of the SG is... There's so much more to it than that.
Ant assists at a higher rate than Sharpe has so far this year. That's not to discount Sharpe, more-so to not discount Ant's ability to make a play for someone else... Historically, Ant as the lead guard makes plays for others at an even higher rate. Sharpe right now has that privilege. Both dudes can play. Sharpe is very capable of playing SG and SF.
"If Ant is too good or too important, play as a small SF and let Sharpe be a proper size SG"... The thing is, positions are situational. So if you're playing Ant and Sharpe together at the wing spots, you don't need to designate them as one or the other because it's about their fit and what the combination of those two guys produces in terms of matchups on both sides of the floor. On defense, it'd make no sense to put Ant on the SF just to say "Yay, we have a big SG because Sharpe is guarding the SG!". When the Blazers are on offense, opposing teams will decide how to guard those two guys based on whatever matchups they want, not what Portland designates those guys as positionally.