That's what the witnesses are for

No it isn't. The role of witnesses is to sign blocks and keep the blockchain secure, control witness variables (such as price feed and now the budget for subsidized accounts), and vote on hard forks. Anything else that witnesses do, especially if expensive, undermines security by reducing the cost of getting voted out (if you spend much or all of your witness rewards to get votes and/or doing things that witnesses are "supposed" to do then there is no economic reason at all to care about getting voted out).

Development is a community responsibility. Steemit has largely taken that on by virtue of having launched the chain in a manner that gave them a dominant portion of the stake, the most funding, and the largest incentive to develop. Still it is absolutely positive if others contribute to development, not just (or even especially) witnesses.

I do think that people who want to fund development using rewards should show evidence of the value add and get widespread support, not just rely on self-voting. (And conversely, rewards being paid out without evidence of value add are fair game for downvoting, self-votes or otherwise.)