Yes, you can do it, I run 2 accounts and only 1 owned 5* sentinel (r4), so I had to use my 4* allotnon the other account. Do I recommend doing full exploration with 4* sentinel as your only champ? No, but he works fine for the majority of content in there, and will be a great asset.
For example of his ability to deal with the problem fights in v3, I used my 4* sentinel to take down biohazard Korg. It takes some skill, but he can do it, and was the only champ I owned that could solo that fight.
Pretty much confirming what Cryptic_Cobra said. Maxed awakened 4 star sentinel is good enough for a cheap completion (coming from personal experience and youtube vids) assuming you have some decent skills. Some paths for exploration look really hard and i wouldn't try them with a 4star unless you are an insanely skilled player and not sure even then.
Yes I'm currently soloing V3 with my 4 Star Rank 5 Sig 40 Sentinel with the Double Cheat Death Synergies of Heimdall and Hela+Angela which also gives you a Permanent 15% Fury, along with either the Permanent Precision Synergy from Heimdall or one of Sentinel's Class Synergies depending on the Fights ahead. I've made it to 3.2, highly suggest beating 3.1 before the Colossus Buff comes out next month because he will then be A LOT HARDER! (He'll be Immune to Incinerate And Armor Break which is Sentinel's main source of Damage)
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For example of his ability to deal with the problem fights in v3, I used my 4* sentinel to take down biohazard Korg. It takes some skill, but he can do it, and was the only champ I owned that could solo that fight.
I've made it to 3.2, highly suggest beating 3.1 before the Colossus Buff comes out next month because he will then be A LOT HARDER! (He'll be Immune to Incinerate And Armor Break which is Sentinel's main source of Damage)