The Warden was the Primal Defender in 4e. It let primal spirits into its body and transformed in all sorts of ways, not just animalistic.
The Warden was 'sticky' by making the space around them difficult terrain, they basically WERE difficult terrain you wanted to avoid.
They could sprout vines and slide people around, and their dailies were powerful forms that granted them buffs and a one time special move. You had forms with evocative names like "Form of the Mauntain's Thunder", "Form of the Dread Serpent", "Form of the Walking Conflagration", "Form of Winter's Herald", "Form of PAradise's Bounty", "Form of the Oak Sentinel" and so forth.
The Warden used either WIS or CON for his AC instead of DEX or INT (as was the default in 4e). 4e also had a ton of conditions that had the mention 'save ends' and basically would keep going until you rolled a 10 or higher on a d20 at the end of your turn. The Warden had an extra roll at the START of his turn, making it FAR more likely to shake off debilitating effects than other classes.
Basically, If I was to make it in 5e I think a subclass of Barbarian COULD do it, provided it was capable of protecting allies and its rage would transform them like Forms.
But a full class could also be possible with the subclass giving access to specific forms and general bonuses.