Windows 95 didn't have concurrency problems different from NT, unless you used it on the old hardware that depended on DOS drivers. The main benefits NT brought were various protection mechanisms, which is convenient for programmers, but 95 surely wasn't slower, especially with less RAM, the major factor that slowed the NT adoption was its significantly higher RAM needs. Which translated in visibly more expensive computers needed. NT was also slower for all graphical routines for a while:

https://en.wikipedia.org/wiki/Architecture_of_Windows_NT

"The Windows NT 3.x series of releases had placed the GDI component in the user-mode Client/Server Runtime Subsystem, but this was moved into kernel mode with Windows NT 4.0 to improve graphics performance.[23]"

Note NT 4.0 appeared a year after Windows 95. The programmers had the benefit of using Windows NT even before 95 appeared, but the advantages of 95 were clear for the "normal users" who didn't think they needed the "protection" aspects: the most popular software of the time (e.g. Microsoft Word) was unstable enough to, from time to time, crash even on NT. The more stable Word versions appeared only after the famous Gates' 2002 memo started to be applied to the Microsoft Office products:

https://en.wikipedia.org/wiki/Trustworthy_computing#Microsof...

Windows 95 was for a time a good trade-off for many practical uses.