Wondering if FFG designers wish that they had preemptively nerfed large ship boost in the same way that large ship barrel rolls were restricted. The Decimator becomes a gal-durn arc dodger with an engine upgrade. In my opinion, a Decimator should not be an arc dodger. BUT, the Aggressor really needs its boost to stay usable.
Maybe two ways to "fix" what may or may not be considered a problem.
1. Engine Upgrade is errata'd to be small ship only. Unambiguous but probably unlikely.
2. Cause large ships to boost using the flat side of a maneuver template Unless that ship comes with boost on its action bar. So EU on large base ship becomes a smaller bump and cannot be used to change direction.
So how terrible an idea is it? I'm sure the answer depends partly on how often you plan on running a large ship with Engine Upgrade.