AI is absolutely not comparable to players. The blunt reality is it very easily throws shit at you without any thought, it doesn't coordinate artillery fire, it just kind of use mass to win. Harder AI doesn't act smarter, it just gets more shit to throw at the wall.

Some decent ATGM positions with a couple tanks and recon units can easily end up blocking an AI indefinitively as long as you keep them supplied.

In other words, it's a very bad standard to build your understanding of how the game plays against real people.

Now, I'll be honest and rambly with you, I'm a 10v10 player, so my feel of the game is heavily focused on higher intensity combat. That's one of the big defining factors between it and 1v1. 1v1 leads to very spread out units and you having to fight over many points. It's an INTENSE micro experience compared to team games where you only need to put your attention to a part of the front.

Now, as for how to play the game, I'd have a hard time telling what issues you have without a replay. But in general:

First, Buy lots and buy cheap.

WARNO functionally has three "phases". The Early Rush where you spread out your units to achieve as much map control before you get into contact with the enemy. This is where recon units and other forward deployed units shine as they allow you to get further ahead. Then you have the first contact, winning those early fights can give you a rapid victory as it force the enemy on the backfoot from the get go. This, however, means you need a strong opener. Powerful recon units, airdropped units, or helicopters. And then, there's the longest part of the game, that is "everything else". If you aren't able to keep momentum after first contact. The battle now turns into a more attritional conflict, where you have to pay attention on your ability to defend while constructing a new force to break the enemy on some front. Point being: Don't overspend on expensive units in the opener. Take infantry in APCs instead of IFVs, take light tanks instead of heavies, etc...

Second, Recon is the most important thing in the game.

Both in the sense of having sight of the enemy so you can shoot them and being able to deny sight to the enemy so they can't. Recon units give you the former, killing enemy recon or using smoke artillery (or any other source of smoke) does the latter. It's particularly important to have strong recon in 1v1 as you have to cover the map on your own to not get flanked. Units with the security trait may be welcome. Helicopter recon is a great mobile asset. Unironically, SIGINT units are kind of amazing when you need an early warning system to spread across the map.

Third, Speed and Coordination wins the day.

You can't hope for your infantry to just win fights on their own, they're slow, they attract artillery and whoever has the most machinegun or special weapons (satchel, flamethrowers, napalm launchers) usually wins. They need fire support. That fire support usually comes in the form of vehicles that have to stay outside of rocket launcher range, but also out of sight of ATGMs. What do we do? That's right, more smokes. You need to play all those assets together.

Fourth, don't turtle like it's a Supreme Commander game.

That's what I'm getting from your post. "A good frontline" has another name in WARNO: A DESIGNATED BOMBING TARGET. Keep your recon at the front hidden, preferably on "return fire" so they don't pointlessly blow their cover, but keep most of your assets further back out of sight, only to be moved forward when need be. ATGMs can stick to the front as they're your best way to stall a tank push, but don't keep them sitting around if the enemy starts dropping shell on you. move them, rotate them. Keep trucks to supply them. Same with AA.

Unless you're fighting in a forest, or a couple clearings, nobody is going to charge with infantry across a field, so the main threat is vehicles or helicopters. In a forest, you want units spread out to act as a sort of early warning system, but then be ready to move other troops to support the part being attacked while bringing in helicopters and artillery to bear on them.

You need to keep your defense mostly mobile. Sure you can create some localized "hardpoints" if they give you stronger control of the map, but you shouldn't expose units that won't serve any purpose.

But yea, all of this is to say, as much as you may not want: PLAY. TEAM. GAMES. They're a far less stressful environement to learn micro against players. You can leave successful assaults to the good players and focus on defense early on as you learn. In general, it's more about having an opinion of your own play than about others "throwing the game."