I've tested summons extensively and most of what you say is true.
The Summons AI waits for your characters 'stance' to go from 'Idle' to 'Combat', and will check for your target. The only way to get them to initiate combat, is to range yourself well outside your own range, press Tab to walk, engage the enemy [while still outside your weapon range], and your summon will approach it. At that point, you click the ground somewhere relatively near the Enemy, and tab again to run. The summon will take the first hit, and pull initial aggro. However, that doesn't solve a large number of issues with the Summon AI.
Here's the full list of things summons needs in a future update.
Need access to 'Taunt' on their special skill cast.
AI routine needs to check more frequently if 2+ enemies are around, to use their specials / AoE's more often. Particularly Taunting.
Should have increase synergy with summoner, possibly protecting them with wards or bubbles, HoT's or other protective buffs periodically.
Need faster or increased Attack Speed scaling.
Specials should be dramatically increased in damage output, as the cast times are normally 3-5 times longer than a basic attack, but only do 1.5x normal damage.
Should check more often which target the summoner is engaging, often times the summon will not change target until the target is dead, leaving the summoner to fend for themselves in DPSing down ADS.
Command Skills; Need a set list of commands like 'Attack', 'Return', 'Defend' and 'Dismiss'.
DoT's of Summons should scale with summon level, or based on 'x' percent of AP the summon has. [Summoner AP increases the pet's AP, allowing you to increase the DoT's directly]
Summons attack ranges need to be set to a minimum of 3m above longest ranged weapon. The reason the summons run back and forth, is their tether range is shorter than their masters attack range. This causes them to constantly boomerang between attacking, and tethering back.