Logic: how could it be possible to answer the question without knowing the skills you picked?!?

Do you have skip attacks?

Turtle is a bit weird right now. There's a frontload of skills that burn your stamina too fast. and many of the stamina saving skills are near the back end. For starters, you absolutely need skip attack, this will almost always save you from gassing out. You should also avoid using skills that let you bypass enemy attack turns. Especially if they have dodge with low strength, because they will spend more time using low-energy blocks and dodges, while you spent all your energy on expensive punches. Only use attack skipping moves if the enemy is losing the energy race, his attacks melt your health bar away, or if his stat build makes it costly to block or dodge. An agi build with high strength, or a turtle with high strength and bearhug will hurt really bad every block they make.

I'm doing turtle at 11 - 7 - 13 right now, been keeping roughly the same stat difference between skills since 6-4-8. It's worked out very well and I've lost just a few fights until taking down Ivangief just now - after about 140 days played on my first playthrough.

Very high agi still give the closest matches in general I guess, but countering their skills and usually dropping my blocking (they bypass it anyways) wins 90%+ even there.

I've done strong arm since the beginning and have almost only punching skills except for the low kick that I almost always use. I'm now ready to get infinite energy in the turtle tree as my next (last?) skill for almost 30 points I think. That should give some hints about how much I've spent along the way. I just took the kick denier skill as well, that really help vs agi as most of them are leg based. (But, I only lost one Agi fight before this that I remember, so you don't need to reach end game to beat them)

Turtle road is the worst of the three, that's said.

Now, if you want to be competitive in this road, you have to Raise mainly your Stamina and Strengh, that the best Duo for this road. You also need to raise a bit of Agility to be able to hit your opponent.
This road is the most demanding in stats (Another proof of how uneven is the game).

Skill wise there is 4 essential skill in this road, you MUST have this skills as soon as possible :
-Skip Attacks (Allow you to keep your energy to a decent level)
-Barrel Strike (It increase your hit chance each time its dodged, must have against agi fighters)
-Spear (Decent Damages/AIM/Energy consumption, and become free to use under 25% energy)
-Bear Strike (Leech ennemy energy when activated, allowing you to litteraly exhaust the opponent, and an exhausted fighter is dead meat)

With these 4 skills, you can honestly beat the game without too much difficulty in turtle road.

-Infinite Energy is not as reliable as it seem, be carefull with it and don't put too much faith in it. In the end, with Skip Attacks, you usually never go under 40-50% energy during mid-late game.
-Bear hugh seem cool, but only against agility fighters, against a strengh fighter, you'll never see the difference, a truck is a truck, it hurt when it hit even if you put an armor.

Finished the game with Turtle now, 173 days on first playthrough. Struggled a bit midgame, but after getting some important skills it was quite easy, didn't lose after going to Russia. About 85% wins total. Ended with 14-9-15 (2 for magic pot).

Gave up trying to train stamina above 13 after getting that perk, impossible when you have to raise the other two as well. I'm happy about choosing the "most difficult" path, was fun :)