spending time to get into top school PhD vs getting done with PhD I have a funded PhD offer from a R1 university in texas but its ranked in the 180s based on USNews, the advisor and myself click very well, he is nice, open-minded, and a young motivated and driven advisor always searching for new collaborations and the research area is in my area of interest. His background is in the sciences and I want to focus on engineering which isn't an issue as there are professors in other depts that I could collaborate with. Finally I will be his only student, he occasionally has undergraduates and his last PhD student will be graduating by the time I get in.

My research focus is in neuroengineering and rehabilitation for movement related disorders - focusing on restoration of grasping and posture. The main difference from top universities is the prestige, level of work (more translational and more grants), will have a better contact base when starting off, many professors working in the area. 

Due to having a low uGPA from India ~ 55%, which is why I applied to mostly masters programs despite having around 2 years of research experience during my undergrad. I feel like I was lucky that the prof had an interest in my profile and asked me to switch to PhD and then I got it (as mentioned in the 1st para). I have also got an MS offer from a 40s ranked university based on USNews with funding only for stipend (would most probably have to take loan for tuition). 

In the hypothetical situation that I take the MS offer I would have to apply for PhDs at the end of my 1st year @ around sept/oct of 2021 and I feel that I would only have a slightly better chance to get into top universities with professors that do amazing work in my area of interest like northwestern, ucsb, rice, university of chicago, and upenn. But at the same time I feel that my horribly low GPA in undergrad will hold me back as I would have to get exceptional grades and do good research; good research seems like an impossible goal in 8 months. Though I may be able to get something useful at the end of my masters but most probably not within 2 semesters. If this scenario of getting into the universities mentioned seems impossible at this point, another option would be to apply to these universities the next year 2022. When I would have finished my masters, but would have to use another extra year working in a research lab and then join the university for PhD.

My question has two parts:
1. The likelihood of getting into the mentioned universities for PhD after 1 year of masters and after 2 years of masters.
2. Is it worth using the 2-3 years to just work towards doing a PhD at these top schools with amazing professors or should I go ahead with PhD straight away and probably think about post-doc with those professors. I just feel that I may miss out on the environment and opportunities that I may get as a student.

Please do not take into consideration about what I want to do in the future like industry, academia etc. as I am set on doing research with these intellectual people and am driven to produce and make an impact on both human knowledge and the patient population (i know this seems like a child's fantasy but this is something that I like to think about) at the end of the day I may go into industry as I am a high-maintanenece person or I may chose to stay in academia as the gratification may overwhelm my needs.
I think you are vastly overestimating the value of ratings from a popular magazine as they apply to doctoral education and vastly underestimating the quality of doctoral education at any R1 in Texas. 

Frankly the real difference, in an individual field between a school rated 180 and one rated, say, 40 is likely to be a mix of random and the value of a given helpful advisor. 

Frankly, I think you would be wasting your time to do much of anything but take what looks like a very nice offer. You'd be halfway through a doctorate at the Texas place before you had a chance to start if you go another route. If you read a lot of questions on this site you'd notice how lucky you would be to have found a good and supportive advisor. Many are not so lucky. Who can say whether you'd have a better time of it if you look elsewhere? 

And it is you that makes your career, not the journalist/researchers at US News rating places on general criteria.