| Modigar |
While I would normally agree with you on Eldritch Guardian not looking all that great, as by itself you're trading two feats for a familiar that lacks the ability scores to actually make use of the combat feats it has access to, and a slightly better version of bravery. If, however, you take a look at the Mauler familiar archetype, and possibly shell out another feat on Improve Familiar later one, it starts to look a lot shinier, as you can quite easily end up with a familiar that can wield weaponry, has enviable physical ability scores, and access to all of your combat feats. For example, if you do this with an imp, it has hands, automatic proficiency with all martial weapons (assuming you haven't picked up an EWP feat), strength 32, and, like the eldritch guardian, almost as many combat feats as a level 20 fighter, which is more than enough to play a not insignificant part in the fight. Eldritch Guardian by itself is useless, but with the Mauler archetype it's terrifying.
Edit: TL,DR: you start off weaker, but you can end up a lot stronger.