This is 100% wrong. In fact, dating back to at least Madden 2004 there was a menu in the staff hiring section of the off-season explicitly dedicated to coach progression and regression where coaches would progress and regress in not only position specific ratings but also ratings in Motivation, Work Ethic, Chemistry, Knowledge, Offense and Defense. The boosts players would receive could also change in accordance to these progressions and regressions. Just simming through one season of Madden 07 just now and I saw my OL and TE boosts go from exclusively +1 AWR to +3 AWR, +2 PBK, and +2 RBK all with the same coaching staff as the year prior.
And if gameplay is the most important aspect you're looking for then definitely go with 17. It is far and away a better game on-the-field than anything offered back then. The only area where I believe those older Madden still outdoes the current Madden's is player movement in terms of respecting speed and momentum but it's not a great enough difference to warrant choosing it over 17 if you're looking for good football.
Off-the-field Madden 07 offers player roles which affects how teams value players based on things like where they were drafted and injury history. It also offers restricted free agency and, as previously mentioned, tangible coaching and medical staffs.
Scouting I would say is a push. 17's is by far easier and more simple but would also require you both to do it before advancing the week at the expense of losing half your alotted scouting points. 07 allows you to play a College All-Star game with incoming rookies which might be interesting but from what I remember it is virtually the only info you get on the players. I much preferred Madden 06's scouting to both.
Trade and draft logic from the AI is absolutely horrid in each. Madden 07 had issues with teams drafting kickers and punters very early (talking first round here) and Madden 17 has
its own litany of issues in that regard. Madden 07 limits you to 10 picks per draft while I believe M17 is somewhere in the 20's.
Progression/Regression is pick your poison. 17 is RPG-based and allows you to do pretty much anything you want with any player and stat chasing plays a significant role in both. It is also absolutely ruthless from a regression standpoint. Once players hit 26 they uniformly start dropping in all physical categories at a rapid pace. And on occasion certain players will suffer nonsensical drops in areas after "bad" games. 07's progression is much more restricted and almost exclusively out of user control and regression is far more friendly.