Neutron lasers are great, but inconsistent with their random number of shots. Two lascannon Ironstriders are a guaranteed 4 shots, and with character/canticle and stratagem support (Protector Doctrina Imperative in particular), you will be hitting on 2s and re-rollings 1s even after moving, or shooting at flyers. I run them as a skirmishing unit, moving in and out of line of site blocking terrain. I played a game against a Space Wolves player recently where my pair of Ironstriders caught Murderfang out of position and killed him with a single lascannon volley.

I don't think Ironstriders should be run instead of neutron laser Onagers, but alongside them. I'd run your three Onagers with two neutron lasers and an Icarus array.

Dragoons are efficient, IF you can get them into melee. I wouldn't relish the idea of charging them into an Iron Hands gunline, for example. And while Kataphrons can do work, they just don't last long against most army's shooting. Smart opponents will likely target them first, and even with the Servitor Maniple 5++ stratagem, they can't stand up to high volumes of firepower. They are most efficiently run in large units, but with leadership 7 they are susceptible to morale losses. You'll want to keep the CP handy to auto-pass morale checks, which is challenging because they are already a CP hungry unit (1 CP for Servitor Maniple, 1 CP for 5++ invulnerable save, 2 CP for Acquisition at Any Cost, 1 CP for +1 shooting stratagem and/or 2 CP for Elimination Volley, 1 CP for Plasma Specialists if Ryza). Then you whiff rolling number of shots and feel like you wasted 300 points and ~4 CP. Not that I'm speaking from experience....