welcome to SQA Stack Exchange.
For the tools JMeter and Locust.IO, you have asked for opinion, which is completely out of scope of this site, as this site excludes opinion based questions.
But just want to shed some light over few concepts. Performance testing is completely independent of the language being used for creating performance scripts. Performance test results or your application performance may depend upon the language and technology used for building the application but not on the language used for testing its Response Time.
In a simple way, if you have to cover a distance of 60 miles then both Motorcycle and Car will take same time if both are running at same speed (remember both are running on different technologies), see what you are comfortable with. Selection of vehicle may depend upon the Budget or width of the road.
As long as any of the tools being considered are used in an efficient and recommended way, there is no difference which you are using. I have worked on JMeter and found it compatible with all types of Web Applications (.Net, JAVA, Wordpress, PHP, SharePoint etc.). But you should see if you are comfortable with using it or not. I have worked on other tools like Grinder, Test Studio, Load Runner.
For selecting a Performance test tool, the important part of the tool lies in the report it provides and how easy it is to understand and analyze, all the effort and time will go in vain, if one is not able to understand or explain the output i.e.
- Where is the bottle neck?
- If performance test is pass or fail?
- If application is supporting required number of users or not?
- Do we need hardware upgrade?
I will say try both the tools (as both are supporting web applications) with your application for some simple scenario (like developers use to print 'Hello World') and then see which one is easy, time saving & understandable to you and suffice your needs, then go for that.