did you use SSD as main drive, games on other drive?
overheating issue?
updated the latest GPU driver?
make sure the game run on your GTX GPU,
sometime battery saving mode or did not plug the powerplug will run in Intel GPU only.

however, confirmed all above~
open task manager and set on top,
roll to CPU usage and run dota2 replay in high graphic.
check on your CPU Ghz...
Normal should be 3.xGhz~4.xGhz
if it drop to 0.xGhz or 1.xGhz mean it's overheating,
and you need replace the thermal paste d.

my GS70 also become lag after sometime gaming and after change thermal and under air-conditioner room,
1hours++ no lagging issue more.
my gs70 spec 4710hq+970m3gb+16gbram+256ssd+1tb hdd for refer.

i think that's the issue,
if you're loading dota2 from same drive will get stucked for a long loading time,
dota may shown error force close msg but just ignore it...
you need load a long time around 1minutes++
and you only using 1 drive, that's mean system and game load at the same time,
your hdd respond time will get a huge delay.
which mean your hdd reach it's peak so getting a slow load and busy traffic when re-cache data making delay/lag/hagging.
here's how you check, open task manager and set on-top
after run dota 2 and go replay or watch people play...
set your eyes on CPU/GPU/HDD usage,
which ever reach 100% means that CPU/GPU/HDD are hitting peak bottle neck need to upgrade.

after checking 100% you should check on CPU Ghz,
if you notice the dota start lagging and the CPU clock Ghz drop to 1.x or 2.2Ghz as example,
this mean it's overheating.

my friend do face the same issue but after he add-on m.2 sata and use sata ssd as main drive, problem solve at 1st.
windows i cannot comment since it due to people liking, some people like windows 8,some 8.1 some windows 10,
so far i don't see big issue from windows 10 recently due to stable upgrading after 1years patch.
*yes,there is 1 update will make your file lost but latest update no problem*

if your ssd memory huge enough, just stuck all the thing u used most into ssd. =D