Wisp tether vs overcharge

Hey guys. I have question about wisp. I saw a lot of skill builds. Someone playing with max tether,someone with max overcharge(of course after spirits) and some playing with max tether and overcharge on 8 lvl. Wisp is my favorite hero in Dota 1 and I always play with max tether after spirits.Soo guys I want to know which one is better and why?
1. 1-2-2-1-2-4-2-1-1-3-4-3-3-3-+4
2. 1-2-2-3-2-4-2-3-3-3-4-1-1-1-+-4
3. 1-2-2-1-2-4-2-3-1-1-4-3-3-3-+-4

Max Tether was good in DotA 1 was because the stun scaled. Now it's not even a stun, it's almost always better to max Overcharge.

Why you think so?

Tether doesn't really scale that well, you get all of the important stuff from 1 point in it.

Overcharge gets massively better as you put more points in it, as it's the same cost for drastically better effects.

Like it's almost better to go stats instead of investing more than 1 point into Tether.

I understand that tether don't have stun after wisp nerf in dota 2,but I think that 100 MS/AS+bonus move speed is much better in early game than damage resist,that killing yourself every second.I used very well tether with chaos knight. Don't think that overcharge is better(100 MS=you can't move) than 1.75 sec MS. You use tether,ck use rift and after 1.75 sec ck will stun enemy and it's easy to kill enemy.

Look:

Tether scales by increasing the slow duration by .5 seconds.

Overcharge gives you and your ally +10 AS, and 5% damage reduction.

Surely Overcharge scales better.

Okay;

20% Damage reduction is huge compared to 5%; given that Io will pump about 400~ ish HP into his partner lets say in a fight, with 20% reduction on that HP, in addition to armour, magic resist ect ect, your target becomes much harder to kill. 5% damage reduction is basically negligible. It also keeps you alive more in team fights, which lets you do your job more, and stay alive, and thus get more gold in fights ect ect. As well as it being a DPS increase

Whereas with Tether you get very minor move-speed increase, and a slightly longer slow duration; But CK, Sven, Tiny, Gyro are all burst heroes, that don't need an extended period of time to get a kill, which means the point has less value. 0.75 seconds is enough given that you already have the move-speed advantage. The attack speed slow maybe? But it's just less certain value compared to Overcharge

Levels on supports are kinda hard to come-by; It's better to get certain value from the point, not potential value.