Enemies don't use dedicated beam kiter builds and AI is very bad at range management. It needs ridiculous combined speed and range advantage to prevent approach by determined player.
Plus, the only beam you really need to keep shield up against is HIL. TL/PL are burst and AI likes linked fire, so you can vent/drop between shots. Gravs/Tacs aren't going to do much to armor during few second of approach.
And as soon as enemies use mixed beam + projectile (Tacs + Gauss on Conquest, etc) advantage of Helmsmanship 3 is lost anyway.
You can't ignore things like missiles or iron beams, or long range high explosive ballistics like maulers. When you are in a Paragon trying to get into close range so you can ensure a kill, those shields have to stay up and that 0 flux boost is almost 2/3rds of your speed (half, when you max everything else). Plus with a 20 second base shield-raise time (5 second max with hull mods, which is still quite slow), you really just want to keep the shield up as much as possible.
If you are being hit by anything hard flux, Helmsmanship 3 fails immediately, so this is hardly an argument for taking it.
You also don't need to raise full shield to fight one enemy. AI always fires exactly at your center anyway + a bit of spread to due to weapon placement/accuracy. With Accelerated Shields hullmod you get enough coverage for long range combat against single enemy in under 1 second, about 3 to fully cover front. Anything above that is excessive unless surrounded.
On narrow ships like Odyssey you might even flicker to prevent shield from expanding too much (and catching shots that would have missed the hull otherwise).
Paragon, 39300 flux, which means you get 393 flux at <1%. 0.34 shield flux/damage means you can take 1155 damage. That's 2 Atropos Torpedoes. Also 2125 dissipation, 10% of which is 212.5, just over half the maximum you can take is dissipated every second. A gauss shot is 1400, so that will end your 0 flux boost (and is slightly more than you can dissipate in DPS as well), but anything less than that and you can keep going. Most Frigates unless they are loaded with all kinetic weapons can't do enough damage to overcome that, so you can actually completely ignore a frigate while you close with a cruiser.
All this damage adds up very quickly if you take it on hull/armor instead, especially if you are talking about blocking high explosive damage like HILs, Pilums, Heavy Maulers etc. That's armor you could use to aggressively vent and kill more enemies.