To be clear I never played an abjurer in a campaign. While working on my curront character I wanted to make a mage tank...What I ended up with is Jiemba, currently 2tempest cleric/3 storw sorcerer, as a hill dwarf so no speed penalty in my chain and I dont have a weapon so im not sure he qualifies as a gish.
For my mage tank, I went with VHuman Fighter 1/Fiend Tomelock 3/Red (or Gold if you're good) Draconic Sorc X in that order of level progression so far. I took the Mobile feat to mitigate the speed penalty, so that I could dump Str and have Dex 14 for better initiative. The pseudo-Disengage also helps out for when enemies get too close with a rapier-using GFB. Otherwise, I'm rocking my +2 RoPK and Hex+Eldritch Spamming, with the occasional Quickened Scorching Ray for beefier opponents. Before taking the bonuses from my magic items into consideration, I'm at 21 AC with plate, shield, and Defense FS. Factor in the Cloak of Protection that I traded for and the +1 on my shield, I'm at 23 AC. Once I DM 7 DDAL/DDEX modules this season, I'll grab a Ring of Protection and be up to 24 AC. Like Jiemba, Z. H. Darkstar is more mage tank than gish, but I do have a weapon option in my back pocket for when the need arises.
Playing him has brought up some interesting questions wten I look at gishes. Namely is it worth using a weapon? If part of your class makes that better than using cantrips for damage then go for it, otherwise dont feel like you have to.
For the most part, I agree with you. This was especially true for the first two seasons. Fortunately thanks to the SCAG cantrips, you can do both roughly equally these days. Here's what Darkstar's non-resource-draining damage options are at 10th level:
Ranged = Eldritch Blast: +9 to hit, (1d10+4)*2 force damage = avg 19 damage
Melee = GFB: +5 to hit, 1d8+2 piercing damge & 1d8+4 fire damage = avg 15 damage
Save-or-hit = Sacred Flame/Vicious Mockery: Dex/Wis DC 17, 2d8/2d4 radiant/psychic damage = avg 9/5 damage
Because of Bounded Accuracy and my RoPK, I've had to rely less on SF/VM these days. Instead, I bust them out when I'm either trying to take advantage of a vulnerability to radiant damage, want the rider effect of VM, or are in a situation where I have disadvantage on my attack rolls.
Now that I've got Elemental Affinity, I'm debating on what I should do for 11th-13th levels. Should I stay the course of my original level progression posted above or take more levels of Warlock? The former keeps me on track for capping out at 8th level Sorc spells at 19th level, granted that most of the spells that I'm taking via Sorc are non-concentration utility spells. The latter caps me at 7th level Sorc spells and 13 SP per long rest at 20th level but bumps my Warlock slots to 3rd level (yielding 2 more SP per short rest), increases Fireball DC +2 by taking the Warlock version, gives me another Eldritch Invocation (Devil's Sight), and grants the extra 1d10 per short rest on an ability check (initiative, which is currently +4) or saving throw (Dex/Wis/Int, which are currently +2/+1/+1 but will be +3/+2/+2 by end of season) via Dark One's Own Luck.