Suggested

DRS "trains"

I don't know if it's my imagination but there seem to be more DRS trains recently and I was trying to think if there was a way of keeping DRS but stopping the trains from happening so often and I think I may have an answer. 
How about putting DRS under the control of development? If it was included with the likes of Acceleration, Braking, Handling etc it would vary how effective it is and therefore reduce the trains. 
I'm not talking about making huge differences between DRS levels, just enough so that if 1 team develops it and another team doesn't, it break the train.
It also gives another key area that needs to be developed and reduces the need to alter the amount of development points needed to max out. 

As an alternative to that approach you could look to real life. Driving closely behind another car results in increased tyre wear. Add that factor to the mix and reduce the disproportionate strength of the DRS effect on lap times and the problem will be solved by drivers being able to post better lap times in clean air than in dirty. DRS trains become less attractive and the racing resembles motor racing rather than the Tour De France cycling peloton. Win-win. 

DRS trains aren't attractive though, find yourself at the back of a 10 car train and the only way to gain places is to boost past at least 8 cars and throw away probably 50% of your boost.
In real life, different teams have different levels of DRS gain, some gaining more, some gaining less. If that was applied here, we'd find some cars getting past and some not.
I know that Tech in HQ and different levels of teams will affect it but obviously not enough but combine it with needing to spend DP on it would make it much more varied. Add in the fact that in order to increase DRS effectiveness you'd need to reduce DP spending in other areas should make for much more diversity among similarly leveled teams

1- train does not provide advantages on every track
2- I've been racing in the rain for 4 days and believe me it's boring without the drs
3- The simplest and cleanest way to avoid runways where Drs is very powerful and try different strategies. now we are racing on 15 tracks
4- vehicle development will increase to 200 points I think it will make a difference

A DRS train doesn't provide an advantage at any track. 
As far as I'm aware, no one mentioned not having DRS 
I'm not entirely sure I understand point 3. I recognise the words, just not the order they're written in😉
It won't make a difference if DRS isn't included in vehicle development though