Acnologia's soul Manipulation isn't a one shot KO, that only happenes after Acno kills the Dragon. He doesn't remove the soul with his normal attacks so him soul haxing Igneel doesn't make much sense.
Also yes, Igneel is comparable but still weaker than Acnologia. As the Dragon Slayer of Magic or whatever, he's naturally resistant as **** to Magic as a whole, and attacking him with it only empowers him hence why the MC didn't nuke him with Etherions years ago. Igneel's attacks would only cease to empower Acnologia, and unlike Igneel Acnologia's Magic resistance, Magic Absorption and such would prove to be a hard counter to Igneel's moveset.
Igneel is comparable to an extent, but even a normal Acnologia would still mid diff Igneel in his prime. Natsu's absolute peak>>> Ignia >>> Igneel imo. Natsu in his 7DS Mode is probably the strongest person in FT until further notice.
Igneel is probably the weakest out of the Dragneel family even in his prime when in comparison to absolute peak Natsu and especially Ignia who just shat out Acnologia level feats causally.